Methods and apparatus to form separators for biocompatible energization elements for biomedical devices

ABSTRACT

Methods and apparatus to form biocompatible energization elements are described. In some examples, the methods and apparatus to form the biocompatible energization elements involve forming cavities composing active cathode chemistry. The active elements of the cathode and anode are sealed with a biocompatible material. In some examples, a field of use for the methods and apparatus may include any biocompatible device or product that requires energization elements.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. ProvisionalApplication No. 62/040,178 filed Aug. 21, 2014 and entitled METHODS ANDAPPARATUS TO FORM BIOCOMPATIBLE ENERGIZATION ELEMENTS FOR BIOMEDICALDEVICES. The contents are relied upon and hereby incorporated byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

Methods and apparatus to form biocompatible energization elements aredescribed. In some examples, the methods and apparatus to form thebiocompatible energization elements involve forming a separator elementof the energization element. The active elements, including anodes,cathodes and electrolytes may be electrochemically connected and mayinteract with the formed separator elements. In some examples, a fieldof use for the methods and apparatus may include any biocompatibledevice or product that requires energization elements.

2. Discussion of the Related Art

Recently, the number of medical devices and their functionality hasbegun to rapidly develop. These medical devices may include, forexample, implantable pacemakers, electronic pills for monitoring and/ortesting a biological function, surgical devices with active components,contact lenses, infusion pumps, and neurostimulators. Addedfunctionality and an increase in performance to many of theaforementioned medical devices has been theorized and developed.However, to achieve the theorized added functionality, many of thesedevices now require self-contained energization means that arecompatible with the size and shape requirements of these devices, aswell as the energy requirements of the new energized components.

Some medical devices may include components such as semiconductordevices that perform a variety of functions and may be incorporated intomany biocompatible and/or implantable devices. However, suchsemiconductor components require energy and, thus, energization elementsshould preferably also be included in such biocompatible devices. Thetopology and relatively small size of the biocompatible devices createsnovel and challenging environments for the enablement of variousfunctionalities. In many examples, it is important to provide a safe,reliable, compact and cost effective means to energize the semiconductorcomponents within the biocompatible devices. Therefore, a need existsfor novel examples of forming biocompatible energization elements forimplantation within or upon biocompatible devices.

SUMMARY OF THE INVENTION

Accordingly, methods and apparatus to form biocompatible energizationelements are disclosed. Implementations include a battery separatorcomprising a hydrogel formulation capable of safe electrode separationin small biocompatible batteries. In some examples, implementations mayprovide a battery including a first and second electrode, an anode, acathode, and a separator, wherein the separator may include a firsthydrogel element or a plurality of hydrogel elements.

In some examples the hydrogel separator comprises a battery thatgenerally includes a first and second electrode. In some examples, theelectrodes may be characterized as an anode electrode and a cathodeelectrode. The battery may also include an anode element, a cathodeelement, and a separator including a permeable hydrogel membrane wherethe separator may be a polymerized layer mixture. The separator may alsoinclude a water soluble polymer/polymeric component. The separator mayalso include a first polymerizable monomer. The separator may alsoinclude a second polymerizable monomer. The separator may also include aliquid solvent.

Implementations may include one or more of the following features;namely, the separator where the water soluble polymer/polymericcomponent is PVP; the separator where the first polymerizable monomer isa hydrophobic polymer with hydrophilic pendant group; the separatorwhere the hydrophobic polymer with hydrophilic pendant group is HEMA theseparator where the second polymerizable monomer is a diestercrosslinking agent; the separator where the diester crosslinking agentis EGDMA; and the separator where the liquid solvent is IPA.

In some examples, implementations may include one or more of thefollowing method features; namely, the method where the water solublepolymer is PVP; the method where the hydrophobic polymer with pendantgroup is HEMA; the method where the diester crosslinking agent is EGDMA;the method where the liquid solvent is IPA; and the method where thephotoinitiator is CGI 819.

One general aspect includes a permeable hydrogel membrane comprising afirst and second electrode, an anode, a cathode, and a separatorcomprising a permeable hydrogel membrane where the separator is apolymerized layer mixture comprising HEMA, and EGDMA. The permeablehydrogel membrane may also include PVP. The permeable hydrogel membranemay also include IPA.

One general aspect includes a method of forming a permeable hydrogelmembrane for use as a separator in a battery including receiving a watersoluble polymer; receiving a hydrophobic polymer with pendant group;receiving a diester crosslinking agent; receiving a liquid solvent;receiving a photoinitiator; mixing the water soluble polymer, thehydrophobic polymer with pendant group, the diester crosslinking agent,and the photoinitiator; and curing the mixture with a heat source.

One general aspect includes a method of forming a permeable hydrogelmembrane for use as a separator in a battery including receiving PVP,receiving HEMA, receiving EGDMA. The method of also includes receivingIPA. The method of also includes receiving CGI 819; and then mixing withPVP, HEMA, EGDMA and IPA. In some examples, after dispensing the mixtureinto the cavity, for example, with a squeegee process, the resultingdeposit may be dried to remove significant amounts of the solvent. Afterdrying, the resulting mixture may be cured, in some examples, with aheat source, an exposure to photons, or with both processes. In someexamples, the exposure to photons may occur where the photons energy isconsistent with a wavelength occurring in the ultraviolet portion of theelectromagnetic spectrum.

One general aspect includes a biomedical device including an insertdevice. The insert device may include a biocompatible energizationelement. This biocompatible energization element also includes a gapspacer layer. The biomedical device also includes a cathode spacer layerand a cathode contact layer. The biomedical device also includes aseparator layer, and at least a first hole in the cathode spacer layerforming a cavity between sides of the hole, the cathode spacer layer andthe separator layer, where the cavity is filled with cathode chemicals.

Implementations may include one or more of the following features;namely, the biomedical device additionally including an electriccircuit; the biomedical device additionally including an electroactiveelement; the biomedical device where the biomedical device is a contactlens; the biomedical device where the biomedical device is a pace maker;and the biomedical device where the biomedical device is an electronicpill.

One general aspect includes a method of forming biocompatibleenergization elements, the method including receiving a first cathodecontact film; forming at least a first cathode can of the first cathodecontact film; receiving a cathode slurry; placing the cathode slurrywithin the cathode can; receiving a first insulating material; receivinga first substrate film of a first insulating material; cutting a hole inthe first substrate film to form a gap spacer layer; laminating a firstsurface of the gap spacer layer to a first surface of the cathode can;receiving a second substrate film of an ionically conductive separatorfilm; cutting a separator shape from the second substrate film; pickingthe separator shape; placing the separator shape within the hole in thefirst substrate film; adhering a portion of the separator shape to aportion of the first surface of the cathode can; receiving an anodefilm; and adhering a second surface of the gap spacer layer to a firstsurface of the anode film.

One general aspect includes a method of forming biocompatibleenergization elements, the method including receiving a cathode contactfilm; forming at least a cathode can in a portion of the cathode contactfilm; receiving a cathode slurry; placing the cathode slurry within thecathode can; receiving a gel forming monomer solution; depositing thegel forming monomer solution within the cathode can; polymerizing thegel forming solution into a gel form separator; adding an electrolytesolution upon the gel form separator; receiving an anode film; andadhering a first surface of the cathode can to a first surface of theanode film.

Implementations may include one or more of the following features. Thebattery where the diester crosslinking agent is ethylene glycoldimethylacrylate (EGDMA). The method where the diester crosslinkingagent is ethylene glycol dimethylacrylate (EGDMA). The method may alsoinclude the method where the dispensing of the mixture includesspreading the mixture with a squeegee type device. The method mayadditionally include singulating an energization element from a laminateassembly where the laminate assembly includes the permeable hydrogelmembrane, bending the singulated energization element into athree-dimensional shape, including the bent singulated energizationelement into an insert, and including the insert into a hydrogel skirtto form a biomedical device.

One general aspect includes a biomedical device apparatus comprising aninsert device having an electroactive element responsive to acontrolling voltage signal. The biomedical device apparatus alsoincludes a circuit electrically connected to a biocompatibleenergization element, where the circuit provides the controlling voltagesignal. The biomedical device apparatus also includes a first and secondelectrode. The biomedical device apparatus also includes an anode. Thebiomedical device apparatus also includes a cathode; and a separatorincluding a permeable hydrogel membrane where the permeable hydrogelmembrane is included of a polymerized mixture including:hydroxyethylmethacrylate (HEMA), ethylene glycol dimethyl acrylate(EGDMA). The biomedical device apparatus also includespolyvinylpyrrolidone (PVP). The biomedical device apparatus alsoincludes isopropyl alcohol (IPA).

One general aspect includes a method of forming a permeable hydrogelmembrane for use as a separator in a battery including receiving a watersoluble polymer; receiving a hydrophobic polymer with hydrophilicpendant group; receiving a diester crosslinking agent; receiving aliquid solvent; receiving a photoinitiator; mixing the water solublepolymer, the hydrophobic polymer with pendant group, the diestercrosslinking agent, and the photoinitiator to form a mixture; dispensingthe mixture onto at least a surface region that is proximate to one ormore of an anode or a cathode of the battery; and curing the dispensedmixture with one or both of a photon source or a heat source.

Implementations may include one or more of the following features. Themethod may include examples where the diester crosslinking agent isethylene glycol dimethylacrylate (EGDMA). The method may also includethe method where the dispensing of the mixture includes spreading themixture with a squeegee type device. The method may also include themethod additionally including singulating an energization element from alaminate assembly where the laminate assembly includes the permeablehydrogel membrane, bending the singulated energization element into athree-dimensional shape, including the bent singulated energizationelement into an insert, and including the insert into a hydrogel skirtto form a biomedical device.

One general aspect includes a method of forming a permeable hydrogelmembrane for use as a separator in a battery including: receivingpolyvinylpyrrolidone (PVP); receiving hydroxyethylmethacrylate (HEMA);receiving ethylene glycol dimethylacrylate (EGDMA); receiving isopropylalcohol (IPA); mixing at least polyvinylpyrrolidone,hydroxyethylmethacrylate, ethylene glycol dimethylacrylate and isopropylalcohol (IPA) to form a mixture; dispensing the mixture onto at least asurface region that is proximate to one or more of an anode or a cathodeof the battery; and curing the dispensed mixture with one or both of aphoton source or a heat source to form the permeable hydrogel membrane.

Implementations may include one or more of the following features. Themethod may include examples where the dispensing of the mixture includesspreading the mixture with a squeegee type device. The method mayadditionally include singulating an energization element from a laminateassembly where the laminate assembly includes the permeable hydrogelmembrane, bending the singulated energization element into athree-dimensional shape, including the bent singulated energizationelement into an insert, and including the insert into a hydrogel skirtto form a biomedical device.

One general aspect includes a biocompatible energization elementcomprising a laminate assembly including a gap spacer layer; a cathodespacer layer; a cathode contact layer; a separator layer; at least afirst hole in the cathode spacer layer forming a cavity between sides ofthe hole, the cathode spacer layer and the separator layer, where thecavity is filled with cathode chemicals. Additionally the separatorlayer may comprise a permeable hydrogel membrane where the permeablehydrogel membrane comprises: hydroxyethylmethacrylate (HEMA), ethyleneglycol dimethylacrylate (EGDMA), polyvinylpyrrolidone (PVP), andisopropyl alcohol (IPA).

One general aspect includes a biomedical device apparatus including aninsert device having an electroactive element responsive to acontrolling voltage signal. The biomedical device apparatus alsoincludes a circuit electrically connected to a biocompatibleenergization element, where the circuit provides the controlling voltagesignal. The biocompatible energization element may include a laminateassembly including a gap spacer layer; a cathode spacer layer; a cathodecontact layer; a separator layer; at least a first hole in the cathodespacer layer forming a cavity between sides of the hole, and theseparator layer. The cavity may be filled with cathode chemicals, andthe separator layer may comprise a permeable hydrogel membrane, wherethe permeable hydrogel membrane is comprised of a polymerized mixtureincluding: a water soluble polymer/polymeric component, a firstpolymerizable monomer, a second polymerizable monomer, and a liquidsolvent.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention will beapparent from the following, more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

FIGS. 1A-1D illustrate exemplary aspects of biocompatible energizationelements in concert with the exemplary application of contact lenses.

FIG. 2 illustrates the exemplary size and shape of individual cells ofan exemplary battery design.

FIG. 3A illustrates a first stand-alone, packaged biocompatibleenergization element with exemplary anode and cathode connections.

FIG. 3B illustrates a second stand-alone, packaged biocompatibleenergization element with exemplary anode and cathode connections.

FIGS. 4A-4N illustrate exemplary method steps for the formation ofbiocompatible energization elements for biomedical devices.

FIG. 5 illustrates an exemplary fully formed biocompatible energizationelement.

FIGS. 6A-6F illustrate exemplary method steps for structural formationof biocompatible energization elements.

FIGS. 7A-7F illustrate exemplary method steps for structural formationof biocompatible energization elements utilizing an alternateelectroplating method.

FIGS. 8A-8H illustrate exemplary method steps for the formation ofbiocompatible energization elements with hydrogel separator forbiomedical devices.

FIGS. 9A-C illustrate exemplary methods steps for structural formationof biocompatible energization elements with alternative hydrogelprocessing examples.

DETAILED DESCRIPTION OF THE INVENTION

Methods and apparatus to form three-dimensional biocompatibleenergization elements are disclosed in this application. The separatorelement within the energization elements may be formed in novel mannersand may include novel materials. In the following sections, detaileddescriptions of various examples are described. The descriptions ofexamples are exemplary embodiments only, and various modifications andalterations may be apparent to those skilled in the art. Therefore, theexamples do not limit the scope of this application. Thethree-dimensional biocompatible energization elements are designed foruse in or proximate to the body of a living organism.

Glossary

In the description and claims below, various terms may be used for whichthe following definitions will apply:

“Anode” as used herein refers to an electrode through which electriccurrent flows into a polarized electrical device. The direction ofelectric current is typically opposite to the direction of electronflow. In other words, the electrons flow from the anode into, forexample, an electrical circuit.

“Binders” as used herein refer to a polymer that is capable ofexhibiting elastic responses to mechanical deformations and that ischemically compatible with other energization element components. Forexample, binders may include electroactive materials, electrolytes,polymers, etc.

“Biocompatible” as used herein refers to a material or device thatperforms with an appropriate host response in a specific application.For example, a biocompatible device does not have toxic or injuriouseffects on biological systems.

“Cathode” as used herein refers to an electrode through which electriccurrent flows out of a polarized electrical device. The direction ofelectric current is typically opposite to the direction of electronflow. Therefore, the electrons flow into the cathode of the polarizedelectrical device and out of, for example, the connected electricalcircuit.

“Coating” as used herein refers to a deposit of material in thin forms.In some uses, the term will refer to a thin deposit that substantiallycovers the surface of a substrate it is formed upon. In other morespecialized uses, the term may be used to describe small thin depositsin smaller regions of the surface.

“Electrode” as used herein may refer to an active mass in the energysource. For example, it may include one or both of the anode andcathode.

“Energized” as used herein refers to the state of being able to supplyelectrical current or to have electrical energy stored within.

“Energy” as used herein refers to the capacity of a physical system todo work. Many uses of the energization elements may relate to thecapacity of being able to perform electrical actions.

“Energy Source” or “Energization Element” or “Energization Device” asused herein refers to any device or layer which is capable of supplyingenergy or placing a logical or electrical device in an energized state.The energization elements may include batteries. The batteries may beformed from alkaline type cell chemistry and may be solid-statebatteries or wet cell batteries.

“Fillers” as used herein refer to one or more energization elementseparators that do not react with either acid or alkaline electrolytes.Generally, fillers may include substantially water insoluble materialssuch as carbon black; coal dust; graphite; metal oxides and hydroxidessuch as those of silicon, aluminum, calcium, magnesium, barium,titanium, iron, zinc, and tin; metal carbonates such as those of calciumand magnesium; minerals such as mica, montmorollonite, kaolinite,attapulgite, and talc; synthetic and natural zeolites such as Portlandcement; precipitated metal silicates such as calcium silicate; hollow orsolid polymer or glass microspheres, flakes and fibers; etc.

“Functionalized” as used herein refers to making a layer or device ableto perform a function including for example, energization, activation,and/or control.

“Mold” as used herein refers to a rigid or semi-rigid object that may beused to form three-dimensional objects from uncured formulations. Someexemplary molds include two mold parts that, when opposed to oneanother, define the structure of a three-dimensional object.

“Power” as used herein refers to work done or energy transferred perunit of time.

“Rechargeable” or “Re-energizable” as used herein refer to a capabilityof being restored to a state with higher capacity to do work. Many usesmay relate to the capability of being restored with the ability to flowelectrical current at a certain rate for certain, reestablished timeperiods.

“Reenergize” or “Recharge” as used herein refer to restoring to a statewith higher capacity to do work. Many uses may relate to restoring adevice to the capability to flow electrical current at a certain ratefor a certain reestablished time period.

“Released” as used herein and sometimes referred to as “released from amold” means that a three-dimensional object is either completelyseparated from the mold, or is only loosely attached to the mold, sothat it may be removed with mild agitation.

“Stacked” as used herein means to place at least two component layers inproximity to each other such that at least a portion of one surface ofone of the layers contacts a first surface of a second layer. In someexamples, a coating, whether for adhesion or other functions, may residebetween the two layers that are in contact with each other through thecoating.

“Traces” as used herein refer to energization element components capableof connecting together the circuit components. For example, circuittraces may include copper or gold when the substrate is a printedcircuit board and may typically be copper, gold or printed film in aflexible circuit. A special type of “Trace” is the current collector.Current collectors are traces with electrochemical compatibility thatmakes the current collector suitable for use in conducting electrons toand from an anode or cathode in the presence of electrolyte.

The methods and apparatus presented herein relate to formingbiocompatible energization elements for inclusion within or on flat orthree-dimensional biocompatible devices. A particular class ofenergization elements may be batteries that are fabricated in layers.The layers may also be classified as laminate layers. A battery formedin this manner may be classified as a laminar battery.

There may be other examples of how to assemble and configure batteriesaccording to the present invention, and some may be described infollowing sections. However, for many of these examples, there areselected parameters and characteristics of the batteries that may bedescribed in their own right. In the following sections, somecharacteristics and parameters will be focused upon.

Exemplary Biomedical Device Construction with Biocompatible EnergizationElements

An example of a biomedical device that may incorporate the EnergizationElements, batteries, of the present invention may be an electroactivefocal-adjusting contact lens. Referring to FIG. 1A, an example of such acontact lens insert may be depicted as contact lens insert 100. In thecontact lens insert 100, there may be an electroactive element 120 thatmay accommodate focal characteristic changes in response to controllingvoltages. The circuit 105, to provide those controlling voltage signalsas well as to provide other function such as controlling sensing of theenvironment for external control signals, may be powered by abiocompatible battery element 110. As depicted in FIG. 1A, the batteryelement 110 may be found as multiple major pieces, in this case threepieces, and may include the various configurations of battery chemistryelements as has been discussed. The battery elements 110 may havevarious interconnect features to join together pieces as may be depictedunderlying the region of interconnect 114. The battery elements 110 maybe connected to a circuit element that may have its own substrate 111upon which interconnect features 125 may be located. A circuit 105,which may be in the form of an integrated circuit, may be electricallyand physically connected to the substrate 111 and its interconnectfeatures 125.

Referring to FIG. 1B, a cross sectional relief of a contact lens 150 mayinclude contact lens insert 100 and its discussed constituents. Thecontact lens insert 100 may be encapsulated into a skirt of contact lenshydrogel 155 which may form encapsulate the insert and provide acomfortable interface of the contact lens 150 to a user's eye.

In reference to concepts of the present invention, the battery elementsmay be formed in a two-dimensional form as depicted in another exampleof FIG. 1C. In this depiction there may be two main regions of batterycells in the regions of battery component 165 and the second batterycomponent in the region of battery chemistry element 160. The batteryelements, which are depicted in flat form in FIG. 1C, may connect to acircuit element 163, which in the example of FIG. 1C may contain twomajor circuit areas 167. The circuit element 163 may connect to thebattery element at an electrical contact 161 and a physical contact 162.The flat structure may be bent into a three-dimensional conicalstructure as has been described in the present invention. In thatprocess a second electrical contact 166 and a second physical contact164 may be used to connect and physically stabilize thethree-dimensional structure. Referring to FIG. 1D, a representation ofthis three-dimensional conical structure 180 may be found. The physicaland electrical contact points 181 may also be found and the illustrationmay be viewed as a three-dimensional view of the resulting structure.This structure may include the modular electrical and battery componentthat will be incorporated with a lens insert into a biocompatibledevice.

Segmented Battery Schemes

Referring to FIG. 2, an example of different types of segmented batteryschemes is depicted for an exemplary battery element for a contact lenstype example. The segmented components may be relatively circular-shaped271, square-shaped 272 or rectangular-shaped. In rectangular-shapedexamples, the rectangles may be small rectangular shapes 273, largerrectangular shapes 274, or even larger rectangular shapes 275.

Custom Shapes of Flat Battery Elements

In some examples of biocompatible batteries, the batteries may be formedas flat elements. Referring to FIG. 3A an example of a rectangularoutline 310 of the battery element may be depicted with an anodeconnection 311 and a cathode connection 312. Referring to FIG. 3B anexample of a circular outline 330 of a battery element may be depictedwith an anode connection 331 and a cathode connection 332.

In some examples of flat-formed batteries, the outlines of the batteryform may be dimensionally and geometrically configured to fit in customproducts. In addition to examples with rectangular or circular outlines,custom “free-form” or “free shape” outlines may be formed which mayallow the battery configuration to be optimized to fit within a givenproduct.

In the exemplary biomedical device case of a variable optic, a“free-form” example of a flat outline may be arcuate in form. The freeform may be of such geometry that when formed to a three-dimensionalshape, it may take the form of a conical, annular skirt that fits withinthe constraining confines of a contact lens. It may be clear thatsimilar beneficial geometries may be formed where medical devices haverestrictive 2D or 3D shape requirements.

Biocompatibility Aspects of Batteries

As an example, the batteries according to the present invention may haveimportant aspects relating to safety and biocompatibility. In someexamples, batteries for biomedical devices should preferably meetrequirements above and beyond those for typical usage scenarios. In someexamples, design aspects may be considered related to stressing events.For example, the safety of an electronic contact lens may need to beconsidered in the event a user breaks the lens during insertion orremoval. In another example, design aspects may consider the potentialfor a user to be struck in the eye by a foreign object. Still furtherexamples of stressful conditions that may be considered in developingdesign parameters and constraints may relate to the potential for a userto wear the lens in challenging environments like the environment underwater or the environment at high altitude in non-limiting examples.

The safety of such a device may be influenced by the materials that thedevice is formed with, by the quantities of those materials employed inmanufacturing the device, and also by the packaging applied to separatethe devices from the surrounding on- or in-body environment. In anexample, pacemakers may be a typical type of biomedical device which mayinclude a battery and which may be implanted in a user for an extendedperiod of time. Accordingly, in some examples, such pacemakers maytypically be packaged with welded, hermetic titanium enclosures, or inother examples, multiple layers of encapsulation. Emerging poweredbiomedical devices may present new challenges for packaging, especiallybattery packaging. These new devices may be much smaller than existingbiomedical devices, for example, an electronic contact lens or pillcamera may be significantly smaller than a pacemaker. In such examples,the volume and area available for packaging may be greatly reduced.

Electrical Requirements of Microbatteries

Another area for design considerations may relate to electricalrequirements of the device upon the battery device. In order to functionas a power source for a medical device, an appropriate battery may needto meet the full electrical requirements of the system when operating ina non-connected or non-externally powered mode. An emerging field ofnon-connected or non-externally powered biomedical devices may include,for example, vision-correcting contact lenses, health monitoringdevices, pill cameras, and novelty devices. Recent developments inintegrated circuit (IC) technology may permit meaningful electricaloperation at very low current levels, for example, picoamps of standbycurrent and microamps of operating current. IC's may also permit verysmall devices.

Microbatteries for biomedical applications may be required to meet manysimultaneous, challenging requirements. For example, the microbatterymay be required to have the capability to deliver a suitable operatingvoltage to an incorporated electrical circuit. This operating voltagemay be influenced by several factors including the IC process “node,”theoutput voltage from the circuit to another device, and a particularcurrent consumption target which may also relate to a desired devicelifetime.

With respect to the IC process, nodes may typically be differentiated bythe minimum feature size of a transistor, such as its “so-called”transistor channel. This physical feature, along with other parametersof the IC fabrication such as gate oxide thickness, may be associatedwith a resulting rating standard for “turn-on” or “threshold” voltagesof field-effect transistors (FET's) fabricated in the given processnode. For example, in a node with a minimum feature size of 0.5 micronsit may be common to find FET's with turn-on voltages of 5.0V. However,at a minimum feature size of 90 nm the FET's may turn-on at 1.2, 1.8,and 2.5V. The IC foundry may supply standard cells of digital blocks,for example, inverters and flip-flops that have been characterized andare rated for use over certain voltage ranges. Designers chose an ICprocess node based on several factors including density of digitaldevices, analog/digital mixed signal devices, leakage current, wiringlayers, and availability of specialty devices such as high-voltageFET's. Given these parametric aspects of the electrical components whichmay draw power from a microbattery, it may be important for themicrobattery power source to be matched to the requirements of thechosen process node and IC design especially in terms of availablevoltage and current.

In some examples, an electrical circuit powered by a microbattery, mayconnect to another device. In non-limiting examples, themicrobattery-powered electrical circuit may connect to an actuator or atransducer. Depending on the application, these may include alight-emitting diode (LED), a sensor, a microelectromechanical system(MEMS) pump, or numerous other such devices. In some examples, suchconnected devices may require higher operating voltage conditions thancommon IC process nodes, for example, a variable-focus lens may require35V to activate. The operating voltage provided by the battery maytherefore be a critical consideration when designing such a system. Insome examples of this type of consideration, the efficiency of a lensdriver to produce 35V from a 1V battery may be significantly less thanit might be when operating from a 2V battery. Further requirements suchas die size may be dramatically different considering the operatingparameters of the microbattery as well.

Individual battery cells may typically be rated with open-circuit,loaded, and cutoff voltages. The open-circuit voltage is the potentialproduced by the battery cell with infinite load resistance. The loadedvoltage is the potential produced by the cell with an appropriate, andtypically also specified, load impedance placed across the cellterminals. The cutoff voltage is typically a voltage at which most ofthe battery has been discharged. The cutoff voltage may represent avoltage, or degree of discharge, below which the battery should not bedischarged to avoid deleterious effects such as excessive gassing. Thecutoff voltage may typically be influenced by the circuit to which thebattery is connected, not just the battery itself, for example, theminimum operating voltage of the electronic circuit. In one example, analkaline cell may have an open-circuit voltage of 1.6V, a loaded voltagein the range 1.0 to 1.5V, and a cutoff voltage of 1.0V. The voltage of agiven microbattery cell design may depend upon other factors of the cellchemistry employed. And, different cell chemistry may therefore havedifferent cell voltages.

Cells may be connected in series to increase voltage; however, thiscombination may come with tradeoffs to size, internal resistance, andbattery complexity. Cells may also be combined in parallelconfigurations to decrease resistance and increase capacity; however,such a combination may tradeoff size and shelf life.

Battery capacity may be the ability of a battery to deliver current, ordo work, for a period of time. Battery capacity may typically bespecified in units such as microamp-hours. A battery which may deliver 1microamp of current for 1 hour has 1 microamp-hour of capacity. Capacitymay typically be increased by increasing the mass (and hence volume) ofreactants within a battery device; however, it may be appreciated thatbiomedical devices may be significantly constrained on available volume.Battery capacity may also be influenced by electrode and electrolytematerial.

Depending on the requirements of the circuitry to which the battery isconnected, a battery may be required to source current over a range ofvalues. During storage prior to active use, a leakage current on theorder of picoamps to nanoamps may flow through circuits, interconnects,and insulators. During active operation, circuitry may consume quiescentcurrent to sample sensors, run timers, and perform such low powerconsumption functions. Quiescent current consumption may be on the orderof nanoamps to milliamps. Circuitry may also have even higher peakcurrent demands, for example, when writing flash memory or communicatingover radio frequency (RF). This peak current may extend to tens ofmilliamps or more. The resistance and impedance of a microbattery devicemay also be important to design considerations.

Shelf life typically refers to the period of time which a battery maysurvive in storage and still maintain useful operating parameters. Shelflife may be particularly important for biomedical devices for severalreasons. Electronic devices may displace non-powered devices, as forexample may be the case for the introduction of an electronic contactlens. Products in these existing market spaces may have establishedshelf life requirements, for example, three years, due to customer,supply chain, and other requirements. It may typically be desired thatsuch specifications not be altered for new products. Shelf liferequirements may also be set by the distribution, inventory, and usemethods of a device including a microbattery. Accordingly,microbatteries for biomedical devices may have specific shelf liferequirements, which may be measured in the number of years for example.

In some examples, three-dimensional biocompatible energization elementmay be rechargeable. For example, an inductive coil may also befabricated on the three-dimensional surface. The inductive coil couldthen be energized with a radio-frequency (“RF”) fob. The inductive coilmay be connected to the three-dimensional biocompatible energizationelement to recharge the energization element when RF is applied to theinductive coil. In another example, photovoltaics may also be fabricatedon the three-dimensional surface and connected to the three-dimensionalbiocompatible energization element. When exposed to light or photons,the photovoltaics will produce electrons to recharge the energizationelement.

In some examples, a battery may function to provide the electricalenergy for an electrical system. In these examples, the battery may beelectrically connected to the circuit of the electrical system. Theconnections between a circuit and a battery may be classified asinterconnects. These interconnects may become increasingly challengingfor biomedical microbatteries due to several factors. In some examples,powered biomedical devices may be very small thus allowing little areaand volume for the interconnects. The restrictions of size and area mayimpact the electrical resistance and reliability of theinterconnections.

In other respects, a battery may contain a liquid electrolyte whichcould boil at high temperature. This restriction may directly competewith the desire to use a solder interconnect which may, for example,require relatively high temperatures such as 250 degrees C. to melt.Although in some examples the battery chemistry, including theelectrolyte, and the heat source used to form solder based interconnectsmay be isolated spatially from each other, in the cases of emergingbiomedical devices, the small size may preclude the separation ofelectrolyte and solder joints by sufficient distance to reduce heatconduction.

Interconnects

Interconnects may allow current to flow to and from the battery inconnection with an external circuit. Such interconnects may interfacewith the environments inside and outside the battery, and may cross theboundary or seal between those environments. These interconnects may beconsidered as traces, making connections to an external circuit, passingthrough the battery seal, and then connecting to the current collectorsinside the battery. As such, these interconnects may have severalrequirements. Outside the battery, the interconnects may resembletypical printed circuit traces. They may be soldered to or otherwiseconnect to other traces. In an example where the battery is a separatephysical element from a circuit board containing an integrated circuit,the battery interconnect may allow for connection to the externalcircuit. This connection may be formed with solder, conductive tape,conductive ink or epoxy, or other means. The interconnect traces mayneed to survive in the environment outside the battery, for example, notcorroding in the presence of oxygen.

As the interconnect passes through the battery seal, it may be ofcritical importance that the interconnect coexist with the seal andpermit sealing. Adhesion may be required between the seal andinterconnect in addition to the adhesion which may be required betweenthe seal and battery package. Seal integrity may need to be maintainedin the presence of electrolyte and other materials inside the battery.Interconnects, which may typically be metallic, may be known as pointsof failure in battery packaging. The electrical potential and/or flow ofcurrent may increase the tendency for electrolyte to “creep” along theinterconnect. Accordingly, an interconnect may need to be engineered tomaintain seal integrity.

Inside the battery, the interconnects may interface with the currentcollectors or may actually form the current collectors. In this regard,the interconnect may need to meet the requirements of the currentcollectors as described herein, or may need to form an electricalconnection to such current collectors.

One class of candidate interconnects and current collectors is metalfoils. Such foils are available in thickness of 25 microns or less,which make them suitable for very thin batteries. Such foil may also besourced with low surface roughness and contamination, two factors whichmay be critical for battery performance. The foils may include zinc,nickel, brass, copper, titanium, other metals, and various alloys.

Electrolyte

An electrolyte is a component of a battery which facilitates a chemicalreaction to take place between the chemical materials of the electrodes.Typical electrolytes may be electrochemically active to the electrodes,for example, allowing oxidation and reduction reactions to occur. Insome examples, this important electrochemical activity may make for achallenge to creating devices that are biocompatible. For example,potassium hydroxide (KOH) may be a commonly used electrolyte in alkalinecells. At high concentration the material has a high pH and may interactunfavorably with various living tissues. On the other hand, in someexamples electrolytes may be employed which may be lesselectrochemically active; however, these materials may typically resultin reduced electrical performance, such as reduced cell voltage andincreased cell resistance. Accordingly, one key aspect of the design andengineering of a biomedical microbattery may be the electrolyte. It maybe desirable for the electrolyte to be sufficiently active to meetelectrical requirements while also being relatively safe for use in- oron-body.

Various test scenarios may be used to determine the safety of batterycomponents, in particular electrolytes, to living cells. These results,in conjunction with tests of the battery packaging, may allowengineering design of a battery system that may meet requirements. Forexample, when developing a powered contact lens, battery electrolytesmay be tested on a human corneal cell model. These tests may includeexperiments on electrolyte concentration, exposure time, and additives.The results of such tests may indicate cell metabolism and otherphysiological aspects. Tests may also include in-vivo testing on animalsand humans.

Electrolytes for use in the present invention may include zinc chloride,zinc acetate, ammonium acetate, and ammonium chloride in massconcentrations from approximately 0.1 percent to 50 percent, and in anon-limiting example may be approximately 25 percent. The specificconcentrations may depend on electrochemical activity, batteryperformance, shelf life, seal integrity, and biocompatibility.

In some examples, several classes of additives may be utilized in thecomposition of a battery system. Additives may be mixed into theelectrolyte base to alter its characteristics. For example, gellingagents such as agar may reduce the ability of the electrolyte to leakout of packing, thereby increasing safety. Corrosion inhibitors may beadded to the electrolyte, for example, to improve shelf life by reducingthe undesired dissolution of the zinc anode into the electrolyte. Theseinhibitors may positively or adversely affect the safety profile of thebattery. Wetting agents or surfactants may be added, for example, toallow the electrolyte to wet the separator or to be filled into thebattery package. Again, these wetting agents may be positive or negativefor safety. The addition of surfactant to the electrolyte may increasethe electrical impedance of the cell, according the lowest concentrationof surfactant to achieve the desired wetting or other properties shouldbe used. Exemplary surfactants may include Triton™ X-100, Triton™ QS44,and Dowfax™ 3B2, all available from the Dow Chemical company, inconcentrations from 0.01 percent to 2 percent.

Novel electrolytes are also emerging which may dramatically improve thesafety profile of biomedical microbatteries. For example, a class ofsolid electrolytes may be inherently resistant to leaking while stilloffering suitable electrical performance.

Batteries using “salt water” electrolyte are commonly used in reservecells for marine use. Torpedoes, buoys, and emergency lights may usesuch batteries. Reserve cells are batteries in which the activematerials, the electrodes and electrolyte, are separated until the timeof use. Because of this separation, the cell's self-discharge is greatlyreduced and shelf life is greatly increased. Salt water batteries may bedesigned from a variety of electrode materials, including zinc,magnesium, aluminum, copper, tin, manganese dioxide, and silver oxide.The electrolyte may be actual sea water, for example, water from theocean flooding the battery upon contact, or may be a speciallyengineered saline formulation. This type of battery may be particularlyuseful in contact lenses. A saline electrolyte may have superiorbiocompatibility to classical electrolytes such as potassium hydroxideand zinc chloride. Contact lenses are stored in a “packing solution”which is typically a mixture of sodium chloride, perhaps with othersalts and buffering agents. This solution has been demonstrated as abattery electrolyte in combination with a zinc anode and manganesedioxide cathode. Other electrolyte and electrode combinations arepossible. A contact lens using a “salt water” battery may contain anelectrolyte based on sodium chloride, packing solution, or even aspecially engineered electrolyte similar to tear fluid. Such a batterycould, for example, be activated with packing solution, maintain anopening to the eye, and continue operating with exposure to human tears.

In addition to or instead of possible benefits for biocompatibility byusing an electrolyte more similar to tears, or actually using tears, areserve cell may be used to meet the shelf life requirements of acontact lens product. Typical contact lenses are specified for storageof 3 years or more. This is a challenging requirement for a battery witha small and thin package. A reserve cell for use in a contact lens mayhave design similar to those shown in FIGS. 1 and 3, but the electrolytewould not be added at the time of manufacture. The electrolyte may bestored in an ampule within the contact lens and connected to thebattery, or saline surrounding the battery may be used as theelectrolyte. Within the contact lens and battery package, a valve orport may be designed to separate the electrolyte from the electrodesuntil the user activates the lens. Upon activation, perhaps by simplypinching the edge of the contact lens similar to activating a glowstick, the electrolyte is allowed to flow into the battery and form anionic pathway between the electrodes. This may involve a one-timetransfer of electrolyte or may expose the battery for continueddiffusion. Some battery systems may use or consume electrolyte duringthe chemical reaction.

Accordingly, it may be necessary to engineer a certain volume ofelectrolyte into the packaged system. This electrolyte may be stored invarious locations including the separator or a reservoir.

In some examples, a design of a battery system may include a componentor components that may function to limit discharge capacity of thebattery system. For example, it may be desirable to design the materialsand amounts of materials of the anode, cathode, or electrolyte such thatone of them may be depleted first during the course of reactions in thebattery system. In such an example, the depletion of one of the anode,cathode or electrode may reduce the potential for problematic dischargeand side reactions to not take place at lower discharge voltages. Theseproblematic reactions may produce, for example, excessive gas orbyproducts which could be detrimental to safety and other factors.

Modular Battery Components

In some examples, a modular battery component may be formed according tosome aspects and examples of the present invention. In these examples,the modular battery assembly may be a separate component from otherparts of the biomedical device. In the example of an ophthalmic contactlens device, such a design may include a modular battery that isseparate from the rest of a media insert. There may be numerousadvantages of forming a modular battery component. For example, in thecase of the contact lens, a modular battery component may be formed in aseparate, non-integrated process which may alleviate the need to handlerigid, three-dimensionally formed optical plastic components. Inaddition, the sources of manufacturing may be more flexible and mayoperate in a more parallel mode to the manufacturing of the othercomponents in the biomedical device. Furthermore, the fabrication of themodular battery components may be decoupled from the characteristics ofthree-dimensional (3D) shaped devices. For example, in applicationsrequiring three-dimensional final forms, a modular battery system may befabricated in a flat or roughly two-dimensional (2D) perspective andthen shaped to the appropriate three-dimensional shape. A modularbattery component may be tested independently of the rest of thebiomedical device and yield loss due to battery components may be sortedbefore assembly. The resulting modular battery component may be utilizedin various media insert constructs that do not have an appropriate rigidregion upon which the battery components may be formed; and, in a stillfurther example, the use of modular battery components may facilitatethe use of different options for fabrication technologies than wouldotherwise be utilized, such as web-based technology (roll to roll),sheet-based technology (sheet-to-sheet), printing, lithography, and“squeegee” processing. In some examples of a modular battery, thediscrete containment aspect of such a device may result in additionalmaterial being added to the overall biomedical device construct. Sucheffects may set a constraint for the use of modular battery solutionswhen the available space parameters require minimized thickness orvolume of solutions.

Battery shape requirements may be driven at least in part by theapplication for which the battery is to be used. Traditional batteryform factors may be cylindrical forms or rectangular prisms, made ofmetal, and may be geared toward products which require large amounts ofpower for long durations. These applications may be large enough thatthey may contain large form factor batteries. In another example, planar(2D) solid-state batteries are thin rectangular prisms, typically formedupon inflexible silicon or glass. These planar solid-state batteries maybe formed in some examples using silicon wafer-processing technologies.In another type of battery form factor, low power, flexible batteriesmay be formed in a pouch construct, using thin foils or plastic tocontain the battery chemistry. These batteries may be made flat (2D),and may be designed to function when bowed to a modest out-of-plane (3D)curvature.

In some of the examples of the battery applications in the presentinvention where the battery may be employed in a variable optic lens,the form factor may require a three-dimensional curvature of the batterycomponent where a radius of that curvature may be on the order ofapproximately 8.4 mm. The nature of such a curvature may be consideredto be relatively steep and for reference may approximate the type ofcurvature found on a human fingertip. The nature of a relative steepcurvature creates challenging aspects for manufacture. In some examplesof the present invention, a modular battery component may be designedsuch that it may be fabricated in a flat, two-dimensional manner andthen formed into a three-dimensional form of relative high curvature.

Battery Module Thickness

In designing battery components for biomedical applications, tradeoffsamongst the various parameters may be made balancing technical, safetyand functional requirements. The thickness of the battery component maybe an important and limiting parameter. For example, in an optical lensapplication the ability of a device to be comfortably worn by a user mayhave a critical dependence on the thickness across the biomedicaldevice. Therefore, there may be critical enabling aspects in designingthe battery for thinner results. In some examples, battery thickness maybe determined by the combined thicknesses of top and bottom sheets,spacer sheets, and adhesive layer thicknesses. Practical manufacturingaspects may drive certain parameters of film thickness to standardvalues in available sheet stock. In addition, the films may have minimumthickness values to which they may be specified base upon technicalconsiderations relating to chemical compatibility, moisture/gasimpermeability, surface finish, and compatibility with coatings that maybe deposited upon the film layers.

In some examples, a desired or goal thickness of a finished batterycomponent may be a component thickness that is less than 220 μm. Inthese examples, this desired thickness may be driven by thethree-dimensional geometry of an exemplary ophthalmic lens device wherethe battery component may need to be fit inside the available volumedefined by a hydrogel lens shape given end user comfort,biocompatibility, and acceptance constraints. This volume and its effecton the needs of battery component thickness may be a function of totaldevice thickness specification as well as device specification relatingto its width, cone angle, and inner diameter. Another important designconsideration for the resulting battery component design may relate tothe volume available for active battery chemicals and materials in agiven battery component design with respect to the resulting chemicalenergy that may result from that design. This resulting chemical energymay then be balanced for the electrical requirements of a functionalbiomedical device for its targeted life and operating conditions

Battery Module Flexibility

Another dimension of relevance to battery design and to the design ofrelated devices that utilize battery based energy sources is theflexibility of the battery component. There may be numerous advantagesconferred by flexible battery forms. For example, a flexible batterymodule may facilitate the previously mentioned ability to fabricate thebattery form in a two-dimensional (2D) flat form. The flexibility of theform may allow the two-dimensional battery to then be formed into anappropriate 3D shape to fit into a biomedical device such as a contactlens.

In another example of the benefits that may be conferred by flexibilityin the battery module, if the battery and the subsequent device isflexible then there may be advantages relating to the use of the device.In an example, a contact lens form of a biomedical device may haveadvantages for insertion/removal of the media insert based contact lensthat may be closer to the insertion/removal of a standard, non-filledhydrogel contact lens.

The number of flexures may be important to the engineering of thebattery. For example, a battery which may only flex one time from aplanar form into a shape suitable for a contact lens may havesignificantly different design from a battery capable of multipleflexures. The flexure of the battery may also extend beyond the abilityto mechanically survive the flexure event. For example, an electrode maybe physically capable of flexing without breaking, but the mechanicaland electrochemical properties of the electrode may be altered byflexure. Flex-induced changes may appear instantly, for example, aschanges to impedance, or flexure may introduce changes which are onlyapparent in long-term shelf life testing.

Battery Module Width

There may be numerous applications into which the biocompatibleenergization elements or batteries of the present invention may beutilized. In general, the battery width requirement may be largely afunction of the application in which it is applied. In an exemplarycase, a contact lens battery system may have constrained needs for thespecification on the width of a modular battery component. In someexamples of an ophthalmic device where the device has a variable opticfunction powered by a battery component, the variable optic portion ofthe device may occupy a central spherical region of about 7.0 mm indiameter. The exemplary battery elements may be considered as athree-dimensional object, which fits as an annular, conical skirt aroundthe central optic and formed into a truncated conical ring. If therequired maximum diameter of the rigid insert is a diameter of 8.50 mm,and tangency to a certain diameter sphere may be targeted (as forexample in a roughly 8.40 mm diameter), then geometry may dictate whatthe allowable battery width may be. There may be geometric models thatmay be useful for calculating desirable specifications for the resultinggeometry which in some examples may be termed a conical frustumflattened into a sector of an annulus.

Flattened battery width may be driven by two features of the batteryelement, the active battery components and seal width. In some examplesrelating to ophthalmic devices a target thickness may be between 0.100mm and 0.500 mm per side, and the active battery components may betargeted at roughly 0.800 mm wide. Other biomedical devices may havediffering design constraints but the principles for flexible flatbattery elements may apply in similar fashion.

Cavities as Design Elements in Battery Component Design

In some examples, battery elements may be designed in manners thatsegment the regions of active battery chemistry. There may be numerousadvantages from the division of the active battery components intodiscrete segments. In a non-limiting example, the fabrication ofdiscrete and smaller elements may facilitate production of the elements.The function of battery elements including numerous smaller elements maybe improved. Defects of various kinds may be segmented andnon-functional elements may be isolated in some cases to result indecreased loss of function. This may be relevant in examples where theloss of battery electrolyte may occur. The isolation of individualizedcomponents may allow for a defect that results in leakage of electrolyteout of the critical regions of the battery to limit the loss of functionto that small segment of the total battery element whereas theelectrolyte loss through the defect could empty a significantly largerregion for batteries configured as a single cell. Smaller cells mayresult in lowered volume of active battery chemicals on an overallperspective, but the mesh of material surrounding each of the smallercells may result in a strengthening of the overall structure.

Battery Element Internal Seals

In some examples of battery elements for use in biomedical devices, thechemical action of the battery involves aqueous chemistry, where wateror moisture is an important constituent to control. Therefore it may beimportant to incorporate sealing mechanisms that retard or prevent themovement of moisture either out of or into the battery body. Moisturebarriers may be designed to keep the internal moisture level at adesigned level, within some tolerance. In some examples, a moisturebarrier may be divided into two sections or components: namely, thepackage and the seal.

The package may refer to the main material of the enclosure. In someexamples, the package may comprise a bulk material. The Water VaporTransmission Rate (WVTR) may be an indicator of performance, with ISO,ASTM standards controlling the test procedure, including theenvironmental conditions operant during the testing. Ideally, the WVTRfor a good battery package may be “zero.” Exemplary materials with anear-zero WVTR may be glass and metal foils. Plastics, on the otherhand, may be inherently porous to moisture, and may vary significantlyfor different types of plastic. Engineered materials, laminates, orco-extrudes may usually be hybrids of the common package materials.

The seal may be the interface between two of the package surfaces. Theconnecting of seal surfaces finishes the enclosure along with thepackage. In many examples, the nature of seal designs may make themdifficult to characterize for the seal's WVTR due to difficulty inperforming measurements using an ISO or ASTM standard, as the samplesize or surface area may not be compatible with those procedures. Insome examples, a practical manner to testing seal integrity may be afunctional test of the actual seal design, for some defined conditions.Seal performance may be a function of the seal material, the sealthickness, the seal length, the seal width, and the seal adhesion orintimacy to package substrates.

In some examples, seals may be formed by welding process that mayinvolve thermal, laser, solvent, friction, ultrasonic, or arcprocessing. In other examples, seals may be formed through the use ofadhesive sealants such as glues, epoxies, acrylics, natural rubber, andsynthetic rubber. Other examples may derive from the utilization ofgasket type material that may be formed from cork, natural and syntheticrubber, polytetrafluoroethylene (PTFE), polypropylene, and silicones tomention a few non-limiting examples.

In some examples, the batteries according to the present invention maybe designed to have a specified operating life. The operating life maybe estimated by determining a practical amount of moisture permeabilitythat may be obtained using a particular battery system and thenestimating when such a moisture leakage may result in an end of lifecondition for the battery. For example, if a battery is stored in a wetenvironment, then the partial pressure difference between inside andoutside the battery will be minimal, resulting in a reduced moistureloss rate, and therefore the battery life may be extended. The sameexemplary battery stored in a particularly dry and hot environment mayhave a significantly reduced expectable lifetime due to the strongdriving function for moisture loss.

Battery Element Separators

Batteries of the type described in the present invention may utilize aseparator material that physically and electrically separates the anodeand anode current collector portions from the cathode and cathodecurrent collector portions. The separator may be a membrane that ispermeable to water and dissolved electrolyte components; however, it maytypically be electrically non-conductive. While a myriad ofcommercially-available separator materials may be known to those ofskill in the art, the novel form factor of the present invention maypresent unique constraints on the task of separator selection,processing, and handling.

Since the designs of the present invention may have ultra-thin profiles,the choice may be limited to the thinnest separator materials typicallyavailable. For example, separators of approximately 25 microns inthickness may be desirable. Some examples which may be advantageous maybe about 12 microns in thickness. There may be numerous acceptablecommercial separators include microfibrillated, microporous polyethylenemonolayer and/or polypropylene-polyethylene-polypropylene (PP/PE/PP)trilayer separator membranes such as those produced by Celgard(Charlotte, N.C.). A desirable example of separator material may beCelgard M824 PP/PE/PP trilayer membrane having a thickness of 12microns. Alternative examples of separator materials useful for examplesof the present invention may include separator membranes includingregenerated cellulose (e.g. cellophane).

While PP/PE/PP trilayer separator membranes may have advantageousthickness and mechanical properties, owing to their polyolefiniccharacter, they may also suffer from a number of disadvantages that mustbe overcome in order to make them useful in examples of the presentinvention. Roll or sheet stock of PP/PE/PP trilayer separator materialsmay have numerous wrinkles or other form errors that may be deleteriousto the micron-level tolerances applicable to the batteries describedherein. Furthermore, polyolefin separators may need to be cut toultra-precise tolerances for inclusion in the present designs, which maytherefore implicate laser cutting as an exemplary method of formingdiscrete current collectors in desirable shapes with tight tolerances.Owing to the polyolefinic character of these separators, certain cuttinglasers useful for micro fabrication may employ laser wavelengths, e.g.355 nm, that will not cut polyolefins. The polyolefins do notappreciably absorb the laser energy and are thereby non-ablatable.Finally, polyolefin separators may not be inherently wettable to aqueouselectrolytes used in the batteries described herein.

Nevertheless, there may be methods for overcoming these inherentlimitations for polyolefinic type membranes. In order to present amicroporous separator membrane to a high-precision cutting laser forcutting pieces into arc segments or other advantageous separatordesigns, the membrane may need to be flat and wrinkle-free. If these twoconditions are not met, the separator membrane may not be fully cutbecause the cutting beam may be inhibited as a result of defocusing ofor otherwise scattering the incident laser energy. Additionally, if theseparator membrane is not flat and wrinkle-free, the form accuracy andgeometric tolerances of the separator membrane may not be sufficientlyachieved. Allowable tolerances for separators of current examples maybe, for example, +0 microns and −20 microns with respect tocharacteristic lengths and/or radii. There may be advantages for tightertolerances of +0 microns and −10 micron and further for tolerances of +0microns and −5 microns. Separator stock material may be made flat andwrinkle-free by temporarily laminating the material to a float glasscarrier with an appropriate low-volatility liquid. Low-volatilityliquids may have advantages over temporary adhesives due to thefragility of the separator membrane and due to the amount of processingtime that may be required to release separator membrane from an adhesivelayer. Furthermore, in some examples achieving a flat and wrinkle-freeseparator membrane on float glass using a liquid has been observed to bemuch more facile than using an adhesive. Prior to lamination, theseparator membrane may be made free of particulates. This may beachieved by ultrasonic cleaning of separator membrane to dislodge anysurface-adherent particulates. In some examples, handling of a separatormembrane may be done in a suitable, low-particle environment such as alaminar flow hood or a cleanroom of at least class 10,000. Furthermore,the float glass substrate may be made to be particulate free by rinsingwith an appropriate solvent, ultrasonic cleaning, and/or wiping withclean room wipes.

While a wide variety of low-volatility liquids may be used for themechanical purpose of laminating microporous polyolefin separatormembranes to a float glass carrier, specific requirements may be imposedon the liquid to facilitate subsequent laser cutting of discreteseparator shapes. One requirement may be that the liquid has a surfacetension low enough to soak into the pores of the separator materialwhich may easily be verified by visual inspection. In some examples, theseparator material turns from a white color to a translucent appearancewhen liquid fills the micropores of the material. It may be desirable tochoose a liquid that may be benign and “safe” for workers that will beexposed to the preparation and cutting operations of the separator. Itmay be desirable to choose a liquid whose vapor pressure may be lowenough so that appreciable evaporation does not occur during the timescale of processing (on the order of 1 day). Finally, in some examplesthe liquid may have sufficient solvating power to dissolve advantageousUV absorbers that may facilitate the laser cutting operation. In anexample, it has been observed that a 12 percent (w/w) solution ofavobenzone UV absorber in benzyl benzoate solvent may meet theaforementioned requirements and may lend itself to facilitating thelaser cutting of polyolefin separators with high precision and tolerancein short order without an excessive number of passes of the cuttinglaser beam. In some examples, separators may be cut with an 8W 355 nmnanosecond diode-pumped solid state laser using this approach where thelaser may have settings for low power attenuation (e.g. 3 percentpower), a moderate speed of 1 to 10 mm/s, and only 1 to 3 passes of thelaser beam. While this UV-absorbing oily composition has been proven tobe an effective laminating and cutting process aid, other oilyformulations may be envisaged by those of skill in the art and usedwithout limitation.

In some examples, a separator may be cut while fixed to a float glass.One advantage of laser cutting separators while fixed to a float glasscarrier may be that a very high number density of separators may be cutfrom one separator stock sheet, much like semiconductor die may bedensely arrayed on a silicon wafer. Such an approach may provide economyof scale and parallel processing advantages inherent in semiconductorprocesses. Furthermore, the generation of scrap separator membrane maybe minimized. Once separators have been cut, the oily process aid fluidmay be removed by a series of extraction steps with miscible solvents,the last extraction may be performed with a high-volatility solvent suchas isopropyl alcohol in some examples. Discrete separators, onceextracted, may be stored indefinitely in any suitable low-particleenvironment.

As previously mentioned polyolefin separator membranes may be inherentlyhydrophobic and may need to be made wettable to aqueous surfactants usedin the batteries of the present invention. One approach to make theseparator membranes wettable may be oxygen plasma treatment. Forexample, separators may be treated for 1 to 5 minutes in a 100 percentoxygen plasma at a wide variety of power settings and oxygen flow rates.While this approach may improve wettability for a time, it may bewell-known that plasma surface modifications provide a transient effectthat may not last long enough for robust wetting of electrolytesolutions. Another approach to improve wettability of separatormembranes may be to treat the surface by incorporating a suitablesurfactant on the membrane. In some cases, the surfactant may be used inconjunction with a hydrophilic polymeric coating that remains within thepores of the separator membrane.

Another approach to provide more permanence to the hydrophilicityimparted by an oxidative plasma treatment may be by subsequent treatmentwith a suitable hydrophilic organosilane. In this manner, the oxygenplasma may be used to activate and impart functional groups across theentire surface area of the microporous separator. The organosilane maythen covalently bond to and/or non-covalently adhere to the plasmatreated surface. In examples using an organosilane, the inherentporosity of the microporous separator may not be appreciably changed,monolayer surface coverage may also be possible and desired. Prior artmethods incorporating surfactants in conjunction with polymeric coatingsmay require stringent controls over the actual amount of coating appliedto the membrane, and may then be subject to process variability. Inextreme cases, pores of the separator may become blocked, therebyadversely affecting utility of the separator during the operation of theelectrochemical cell. An exemplary organosilane useful in the presentinvention may be (3-aminopropyl)triethoxysilane. Other hydrophilicorganosilanes may be known to those of skill in the art and may be usedwithout limitation.

Still another method for making separator membranes wettable by aqueouselectrolyte may be the incorporation of a suitable surfactant in theelectrolyte formulation. One consideration in the choice of surfactantfor making separator membranes wettable may be the effect that thesurfactant may have on the activity of one or more electrodes within theelectrochemical cell, for example, by increasing the electricalimpedance of the cell. In some cases, surfactants may have advantageousanti-corrosion properties, specifically in the case of zinc anodes inaqueous electrolytes. Zinc may be an example known to undergo a slowreaction with water to liberate hydrogen gas, which may be undesirable.Numerous surfactants may be known by those of skill in the art to limitrates of the reaction to advantageous levels. In other cases, thesurfactant may so strongly interact with the zinc electrode surface thatbattery performance may be impeded. Consequently, much care may need tobe made in the selection of appropriate surfactant types and loadinglevels to ensure that separator wettability may be obtained withoutdeleteriously affecting electrochemical performance of the cell. In somecases, a plurality of surfactants may be used, one being present toimpart wettability to the separator membrane and the other being presentto facilitate anti-corrosion properties to the zinc anode. In oneexample, no hydrophilic treatment is done to the separator membrane anda surfactant or plurality of surfactants is added to the electrolyteformulation in an amount sufficient to effect wettability of theseparator membrane.

Discrete separators may be integrated into the laminar microbattery bydirect placement into a designed cavity, pocket, or structure within theassembly. Desirably, this pocket may be formed by a spacer having acutout that may be a geometric offset of the separator shape.Furthermore, the pocket may have a ledge or step on which the separatorrests during assembly. The ledge or step may optionally include apressure-sensitive adhesive which retains the discrete separator.Advantageously, the pressure-sensitive adhesive may be the same one usedin the construction and stack up of other elements of an exemplarylaminar microbattery.

Pressure Sensitive Adhesive

In some examples, the plurality of components comprising the laminarmicrobatteries of the present invention may be held together with apressure-sensitive adhesive (PSA) that also serves as a sealant. While amyriad of commercially available pressure-sensitive adhesiveformulations may exist, such formulations almost always includecomponents that may make them unsuitable for use within a biocompatiblelaminar microbattery. Examples of undesirable components inpressure-sensitive adhesives may include low molecular mass leachablecomponents, antioxidants e.g. BHT and/or MEHQ, plasticizing oils,impurities, oxidatively unstable moieties containing for exampleunsaturated chemical bonds, residual solvents and/or monomers,polymerization initiator fragments, polar tackifiers, and the like.

Suitable PSAs may on the other hand exhibit the following properties.They may be able to be applied to laminar components to achieve thinlayers on the order of 2 to 20 microns. As well, they may contain aminimum of, for example, zero undesirable or non-biocompatiblecomponents. Additionally, they may have sufficient adhesive and cohesiveproperties so as to bind the components of the laminar battery together.And, they may be able to flow into the micron-scale features inherent indevices of the present construction while providing for a robust sealingof electrolyte within the battery. In some examples of suitable PSAs,the PSAs may have a low permeability to water vapor in order to maintaina desirable aqueous electrolyte composition within the battery even whenthe battery may be subjected to extremes in humidity for extendedperiods of time. The PSAs may have good chemical resistance tocomponents of electrolytes such as acids, surfactants, and salts. Theymay be inert to the effects of water immersion. Suitable PSAs may have alow permeability to oxygen to minimize the rate of direct oxidation,which may be a form of self-discharge, of zinc anodes. And, they mayfacilitate a finite permeability to hydrogen gas, which may be slowlyevolved from zinc anodes in aqueous electrolytes. This property offinite permeability to hydrogen gas may avoid a build-up of internalpressure.

In consideration of these requirements, polyisobutylene (PIB) may be acommercially-available material that may be formulated into PSAcompositions meeting many if not all desirable requirements.Furthermore, PIB may be an excellent barrier sealant with very low waterabsorbance and low oxygen permeability. An example of PIB useful in theexamples of the present invention may be Oppanol® B15 by BASFCorporation. Oppanol° B15 may be dissolved in hydrocarbon solvents suchas toluene, dodecane, mineral spirits, and the like. One PSA compositionmay include 30 percent Oppanol® B15 (w/w) in a solvent mixture including70 percent (w/w) toluene and 30 percent dodecane. The adhesive andrheological properties of PIB based PSA's may be determined in someexamples by the blending of different molecular mass grades of PIB. Acommon approach may be to use a majority of low molar mass PIB, e.g.Oppanol® B10 to effect wetting, tack, and adhesion, and to use aminority of high molar mass PIB to effect toughness and resistance toflow. Consequently, blends of any number of PIB molar mass grades may beenvisioned and may be practiced within the scope of the presentinvention. Furthermore, tackifiers may be added to the PSA formulationso long as the aforementioned requirements may be met. By their verynature, tackifiers impart polar properties to PSA formulations, so theymay need to be used with caution so as to not adversely affect thebarrier properties of the PSA. Furthermore, tackifiers may in some casesbe oxidatively unstable and may include an antioxidant, which couldleach out of the PSA. For these reasons, examplary tackifiers for use inPSA's for biocompatible laminar microbatteries may include fully- ormostly hydrogenated hydrocarbon resin tackifiers such as the Regalrezseries of tackifiers from Eastman Chemical Corporation.

Additional Package and Substrate Considerations in Biocompatible BatteryModules

There may be numerous packaging and substrate considerations that maydictate desirable characteristics for package designs used inbiocompatible laminar microbatteries. For example, the packaging maydesirably be predominantly foil and/or film based where these packaginglayers may be as thin as possible, for example, 10 to 50 microns.Additionally, the packaging may provide a sufficient diffusion barrierto moisture gain or loss during the shelf life. In many desirableexamples, the packaging may provide a sufficient diffusion barrier tooxygen ingress to limit degradation of zinc anodes by direct oxidation.

In some examples, the packaging may provide a finite permeation pathwayto hydrogen gas that may evolve due to direct reduction of water byzinc. And, the packaging may desirably sufficiently contain and mayisolate the contents of the battery such that potential exposure to auser may be minimized.

In the present invention, packaging constructs may include the followingtypes of functional components; namely, top and bottom packaging layers,PSA layers, spacer layers, interconnect zones, filling ports, andsecondary packaging.

In some examples, top and bottom packaging layers may comprise metallicfoils or polymer films. Top and bottom packaging layers may comprisemulti-layer film constructs comprised of a plurality of polymer and/orbarrier layers. Such film constructs may be referred to as coextrudedbarrier laminate films. An example of a commercial coextruded barrierlaminate film of particular utility in the present invention may be 3M®Scotchpak 1109 backing which consists of a polyethylene terephthalate(PET) carrier web, a vapor-deposited aluminum barrier layer, and apolyethylene layer including a total average film thickness of 33microns. Numerous other similar multilayer barrier films may beavailable and may be used in alternate examples of the presentinvention.

In design constructions including a PSA, packaging layer surfaceroughness may be of particular importance because the PSA may also needto seal opposing packaging layer faces. Surface roughness may resultfrom manufacturing processes used in foil and film production, forexample, processes employing rolling, extruding, embossing and/orcalendaring, among others. If the surface is too rough, PSA may be notable to be applied in a uniform thickness when the desired PSA thicknessmay be on the order of the surface roughness Ra. Furthermore, PSA's maynot adequately seal against an opposing face if the opposing face hasroughness that may be on the order of the PSA layer thickness. In thepresent invention, packaging materials having a surface roughness, Ra,less than 10 microns may be acceptable examples. In some examples,surface roughness values may be 5 microns or less. And, in still furtherexamples, the surface roughness may be 1 micron or less. Surfaceroughness values may be measured by a variety of methods including butnot limited to measurement techniques such as white lightinterferometry, stylus profilometry, and the like. There may be manyexamples in the art of surface metrology that surface roughness may bedescribed by a number of alternative parameters and that the averagesurface roughness, Ra, values discussed herein may be meant to berepresentative of the types of features inherent in the aforementionedmanufacturing processes.

Current Collectors and Electrodes

In some examples of zinc-carbon and Leclanché cells, the cathode currentcollector may be a sintered carbon rod. This type of material may facetechnical hurdles for thin electrochemical cells of the presentinvention. In some examples, printed carbon inks may be used in thinelectrochemical cells to replace a sintered carbon rod for the cathodecurrent collector, and in these examples, the resulting device may beformed without significant impairment to the resulting electrochemicalcell. Typically, the carbon inks may be applied directly to packagingmaterials which may include polymer films, or in some cases metal foils.In the examples where the packaging film may be a metal foil, the carbonink may need to protect the underlying metal foil from chemicaldegradation and/or corrosion by the electrolyte. Furthermore, in theseexamples, the carbon ink current collector may need to provideelectrical conductivity from the inside of the electrochemical cell tothe outside of the electrochemical cell, implying sealing around orthrough the carbon ink. Due to the porous nature of carbon inks, thismay be not easily accomplished without significant challenges. Carboninks also may be applied in layers that have finite and relatively smallthickness, for example, 10 to 20 microns. In a thin electrochemical celldesign in which the total internal package thickness may only be about100 to 150 microns, the thickness of a carbon ink layer may take up asignificant fraction of the total internal volume of the electrochemicalcell, thereby negatively impacting electrical performance of the cell.Further, the thin nature of the overall battery and the currentcollector in particular may imply a small cross-sectional area for thecurrent collector. As resistance of a trace increases with trace lengthand decreases with cross-sectional already, there may be a directtradeoff between current collector thickness and resistance. The bulkresistivity of carbon ink may be insufficient to meet the resistancerequirement of thin batteries. Inks filled with silver or otherconductive metals may also be considered to decrease resistance and/orthickness, but they may introduce new challenges such as incompatibilitywith novel electrolytes. In consideration of these factors, in someexamples it may be desirable to realize efficient and high performancethin electrochemical cells of the present invention by utilizing a thinmetal foil as the current collector, or to apply a thin metal film to anunderlying polymer packaging layer to act as the current collector. Suchmetal foils may have significantly lower resistivity, thereby allowingthem to meet electrical resistance requirements with much less thicknessthan printed carbon inks.

In some examples, one or more of the top and/or bottom packaging layersmay serve as a substrate for a sputtered current collector metal ormetal stack. For example, 3M® Scotchpak 1109 backing may be metallizedusing physical vapor deposition (PVD) of one or more metallic layersuseful as a current collector for a cathode. Exemplary metal stacksuseful as cathode current collectors may be Ti—W (Titanium-Tungsten)adhesion layers and Ti (Titanium) conductor layers. Exemplary metalstacks useful as anode current collectors may be Ti—W adhesion layers,Au (Gold) conductor layers, and In (Indium) deposition layers. Thethickness of the PVD layers may be, for example, less than 500 nm intotal. If multiple layers of metals are used, the electrochemical andbarrier properties may need to be compatible with the battery. Forexample, copper may be electroplated on top of a seed layer to grow athick layer of conductor. Additional layers may be plated upon thecopper. However, copper may be electrochemically incompatible withcertain electrolytes especially in the presence of zinc. Accordingly, ifcopper is used as a layer in the battery, it may need to be sufficientlyisolated from the battery electrolyte. Alternatively, copper may beexcluded or another metal substituted.

In some other examples, top and/or bottom packaging foils may alsofunction as current collectors. For example, a 25 micron brass foil maybe useful as an anode current collector for a zinc anode. The brass foilmay be optionally electroplated with indium prior to electroplating withzinc. In one example, cathode current collector packaging foils mayinclude titanium foil, Hastelloy C-276 foil, chromium foil, and/ortantalum foil. In certain designs, one or more packaging foils may befine blanked, embossed, etched, textured, laser machined, or otherwiseprocessed to provide desirable form, surface roughness, and/or geometryto the final cell packaging.

Anode and Anode Corrosion Inhibitors

The anode for the laminar battery of the present invention may includezinc. In traditional zinc-carbon batteries, a zinc anode may take thephysical form of a can in which the contents of the electrochemical cellmay be contained. For the battery of the present invention, a zinc canmay be an example but there may be other physical forms of zinc that mayprovide desirable to realize ultra-small battery designs.

Electroplated zinc may have examples of use in a number of industries,for example, for the protective or aesthetic coating of metal parts. Insome examples, electroplated zinc may be used to form thin and conformalanodes useful for batteries of the present invention. Furthermore, theelectroplated zinc may be patterned in seemingly endless configurations,depending on the design intent. A facile means for patterningelectroplated zinc may require processing with the use of a photomask ora physical mask. A plating mask may be fabricated by a variety ofapproaches. One approach may be by using a photomask. In these examples,a photoresist may be applied to a conductive substrate, the substrate onwhich zinc may subsequently be plated. The desired plating pattern maybe then projected to the photoresist by means of a photomask, therebycausing curing of selected areas of photoresist. The uncured photoresistmay then be removed with appropriate solvent and cleaning techniques.The result may be a patterned area of conductive material that mayreceive an electroplated zinc treatment. While this method may providebenefit to the shape or design of the zinc to be plated, the approachmay require use of available photopatternable materials, which may haveconstrained properties to the overall cell package construction.Consequently, new and novel methods for patterning zinc may be requiredto realize some designs of thin microbatteries of the present invention.

An alternative means of patterning zinc anodes may be by means of aphysical mask application. A physical mask may be made by cuttingdesirable apertures in a film having desirable barrier and/or packagingproperties. Additionally, the film may have pressure-sensitive adhesiveapplied to one or both sides. Finally, the film may have protectiverelease liners applied to one or both adhesives. The release liner mayserve the dual purpose of protecting the adhesive during aperturecutting and protecting the adhesive during specific processing steps ofassembling the electrochemical cell, specifically the cathode fillingstep, described in following description. In some examples, a zinc maskmay comprise a PET film of approximately 100 microns thickness to whicha pressure-sensitive adhesive may be applied to both sides in a layerthickness of approximately 10-20 microns. Both PSA layers may be coveredby a PET release film which may have a low surface energy surfacetreatment, and may have an approximate thickness of 50 microns. In theseexamples, the multi-layer zinc mask may comprise PSA and PET film. PETfilms and PET/PSA zinc mask constructs as described herein may bedesirably processed with precision nanosecond laser micromachiningequipment, for example, an Oxford Lasers E-Series laser micromachiningworkstation, to create ultra-precise apertures in the mask to facilitatelater plating. In essence, once the zinc mask has been fabricated, oneside of the release liner may be removed, and the mask with aperturesmay be laminated to the anode current collector and/or anode-sidepackaging film/foil. In this manner, the PSA creates a seal at theinside edges of the apertures, facilitating clean and precise masking ofthe zinc during electroplating.

The zinc mask may be placed and then electroplating of one or moremetallic materials may be performed. In some examples, zinc may beelectroplated directly onto an electrochemically compatible anodecurrent collector foil such as brass. In alternate design examples wherethe anode side packaging includes a polymer film or multi-layer polymerfilm upon which seed metallization has been applied, zinc, and/or theplating solutions used for depositing zinc, may not be chemicallycompatible with the underlying seed metallization. Manifestations oflack of compatibility may include film cracking, corrosion, and/orexacerbated H2 evolution upon contact with cell electrolyte. In such acase, additional metals may be applied to the seed metal to effectbetter overall chemical compatibility in the system. One metal that mayfind particular utility in electrochemical cell constructions may beindium. Indium may be widely used as an alloying agent in battery gradezinc with its primary function being to provide an anti-corrosionproperty to the zinc in the presence of electrolyte. In some examples,indium may be successfully deposited on various seed metallizations suchas Ti—W and Au. Resulting films of 1-3 microns of indium on the seedmetallization layers may be low-stress and adherent. In this manner, theanode-side packaging film and attached current collector having anindium top layer may be conformable and durable. In some examples, itmay be possible to deposit zinc on an indium-treated surface, theresulting deposit may be very non-uniform and nodular. This effect mayoccur at lower current density settings, for example 20 ASF. As viewedunder a microscope, nodules of zinc may be observed to form on theunderlying smooth indium deposit. In certain electrochemical celldesigns, the vertical space allowance for the zinc anode layer may be upto about 5-10 microns maximum, but in some examples, lower currentdensities may be used for zinc plating, and the resulting nodulargrowths may grow taller than the maximum anode vertical allowance. Itmay be that the nodular zinc growth stems from a combination of the highoverpotential of indium and the presence of an oxide layer of indium.

In some examples, higher current density DC plating may overcome therelatively large nodular growth patterns of zinc on indium surfaces. Forexample, 100 ASF plating conditions may result in nodular zinc, but thesize of the zinc nodules may be drastically reduced compared to 20 ASFplating conditions. Furthermore, the number of nodules may be vastlygreater under 100 ASF plating conditions. The resulting zinc film mayultimately coalesce to a more or less uniform layer with only someresidual feature of nodular growth while meeting the vertical spaceallowance of about 5-10 microns.

An added benefit of indium in the electrochemical cell may be reductionof hydrogen gas, which may be a slow process that occurs in aqueouselectrochemical cells containing zinc. The indium may be beneficiallyapplied to one or more of the anode current collector, the anode itselfas a co-plated alloying component, or as a surface coating on theelectroplated zinc. For the latter case, indium surface coatings may bedesirably applied in situ by way of an electrolyte additive such asindium trichloride or indium acetate. When such additives may be addedto the electrolyte in small concentrations, indium may spontaneouslyplate on exposed zinc surfaces as well as portions of exposed anodecurrent collector.

Zinc, and similar anodes commonly used in commercial primary batteries,is typically found in sheet, rod, and paste forms. The anode of aminiature, biocompatible battery may be of similar form, e.g. thin foil,or may be plated as previously mentioned. The properties of this anodemay differ significantly from those in existing batteries, for example,because of differences in contaminants or surface finish attributed tomachining and plating processes. Accordingly, the electrodes andelectrolyte may require special engineering to meet capacity, impedance,and shelf life requirements. For example, special plating processparameters, plating bath composition, surface treatment, and electrolytecomposition may be needed to optimize electrode performance.

Cathode Mix

There may be numerous cathode chemistry mixes that may be consistentwith the concepts of the present invention. In some examples, a cathodemix, which may be a term for a chemical formulation used to form abattery's cathode, may be applied as a paste or slurry and may includemanganese dioxide, some form of conductive carbon such as carbon blackor graphite, and other optional components. In some examples, theseoptional components may include one or more of binders, electrolytesalts, corrosion inhibitors, water or other solvents, surfactants,rheology modifiers, and other conductive additives, for example,conductive polymers. Once formulated and appropriately mixed, thecathode mix may have a desirable rheology that allows it to either bedispensed onto desired portions of the separator and/or cathode currentcollector, or squeegeed through a screen or stencil in a similar manner.In some examples, the cathode mix may be dried prior to later cellassembly steps, while in other examples, the cathode may contain some orall of the electrolyte components, and may only be partially dried to aselected moisture content.

The manganese dioxide which may be used in the cathode mix may be, forexample, electrolytic manganese dioxide (EMD) due to the beneficialadditional energy capacity that this type of manganese dioxide providesrelative to other forms such as natural manganese dioxide or chemicalmanganese dioxide. Furthermore, the EMD useful in batteries of thepresent invention may need to have a particle size and particle sizedistribution that may be conductive to the formation of depositable orprintable cathode mix pastes/slurries. Specifically, the EMD may beprocessed to remove significant large particulate components that wouldbe considered large relative to other features such as battery internaldimensions, separator thicknesses, dispense tip diameters, stencilopening sizes, or screen mesh sizes. In some examples, EMD may have anaverage particle size of 7 microns with a large particle content thatmay contain particulates up to about 70 microns. In alternativeexamples, the EMD may be sieved, further milled, or otherwise separatedor processed to limit large particulate content to below a certainthreshold, for example, 25 microns or smaller. One process useful forthe particle size reduction of EMD may be jet milling where sub-micronparticulate may be obtained. Other processes useful for large particlesize reduction may include ball milling or 3-roll milling of the cathodemix paste prior to use.

A critical aspect of the cathode mix paste may be the polymeric binder.The binder may serve a number of functions in the cathode mix paste. Theprimary function of the binder may be to create a sufficientinter-particle electrical network between EMD particles and carbonparticles. A secondary function of the binder may be to facilitateelectrical contact to the cathode current collector. A third function ofthe binder may be to influence the rheological properties of the cathodemix paste for advantageous dispensing and/or stenciling/screening.Still, a fourth function of the binder may be to enhance the electrolyteuptake and distribution within the cathode. The choice of the binderpolymer as well as the specific amount to be used may be critical to thebeneficial function of the cathode in the electrochemical cell of thepresent invention. If the binder polymer is too soluble in theelectrolyte to be used, then the primary function of the binder,electrical continuity, may be drastically impacted to the point of cellnon-functionality. On the contrary, if the binder polymer is insolublein the electrolyte to be used, portions of EMD may be ionicallyinsulated from the electrolyte, resulting in diminished cell performancesuch as reduced capacity, lower open circuit voltage, and/or increasedinternal resistance. In the end, choice of binder polymer and amount tobe used may be a careful balancing act that may need to be determined bycareful experimentation, in some examples using the design ofexperiments (DOE) approach. Examples of binder polymers useful for thepresent invention include polyvinylpyrrolidone, polyisobutylene, rubberytriblock copolymers (including styrene end blocks such as thosemanufactured by Kraton Polymers), styrene-butadiene latex blockcopolymers, polyacrylic acid, hydroxyethylcellulose,carboxymethylcellulose, dispersion polymers such as latexes,polytetrafluoroethylene, polyethylene, among other examples of binderpolymers.

The cathode may also comprise silver dioxide or nickel oxyhydroxide,among other candidate materials. Such materials may offer increasedcapacity and less decrease in loaded voltage during discharge relativeto manganese dioxide, both desirable properties in a battery. Batteriesbased on these cathodes may have current examples present in industryand literature. A novel microbattery utilizing a silver dioxide cathodemay include a biocompatible electrolyte, for example one including zincchloride and/or ammonium chloride instead of potassium hydroxide.

Battery Architecture and Fabrication

Battery architecture and fabrication technology may be closelyintertwined. As has been discussed in earlier sections of the presentdisclosure, a battery has the following elements: cathode, anode,separator, electrolyte, cathode current collector, anode currentcollector, and packaging. Clever design may try to combine theseelements in easy to fabricate subassemblies. In other examples,optimized design may have dual-use components, for example, using ametal package to double as a current collector. From a relative volumeand thickness standpoint, these elements may be nearly all the samevolume, except for the cathode. In some examples, the electrochemicalsystem may require about two (2) to ten (10) times the volume of cathodeas anode due to significant differences in mechanical density, energydensity, discharge efficiency, material purity, and the presence ofbinders, fillers, and conductive agents. In these examples, the relativescale of the various components may be approximated in the followingthicknesses of the elements: Anode current collector=1 μm; Cathodecurrent collector=1 μm; Electrolyte=interstitial liquid (effectively 0μm); Separator=as thin or thick as desired where the planned maximalthickness may be about 15 μm; Anode=5 μm; and the Cathode=50 μm. Forthese examples of elements the packaging needed to provide sufficientprotection to maintain battery chemistry in use environments may have aplanned maximal thickness of about 50 μm.

In some examples, which may be fundamentally different from large,prismatic constructs such as cylindrical or rectangular forms and whichmay be different than wafer-based solid state construct, such examplesmay assume a “pouch”-like construct, using webs or sheets fabricatedinto various configurations, with battery elements arranged inside. Thecontainment may have two films or one film bent over onto the otherside, either configuration of which may form two roughly planarsurfaces, which may be then sealed on the perimeter to form a container.This thin-but-wide form factor may make battery elements themselves thinand wide. Furthermore, these examples may be suitable for applicationthrough coating, gravure printing, screen printing, sputtering, or othersimilar fabrication technology.

There may be numerous arrangements of the internal components, such asthe anode, separator and cathode, in these “pouch-like” battery exampleswith thin-but-wide form factor. Within the enclosed region formed by thetwo films, these basic elements may be either “co-planar” that isside-by-side on the same plane or “co-facial” which may be face-to-faceon opposite planes. In the co-planar arrangement, the anode, separator,and cathode may be deposited on the same surface. For the co-facialarrangement, the anode may be deposited on surface-1, the cathode may bedeposited on surface-2, and the separator may be placed between the two,either deposited on one of the sides, or inserted as its own separateelement.

Another type of example may be classified as laminate assembly, whichmay involve using films, either in a web or sheet form, to build up abattery layer by layer. Sheets may be bonded to each other usingadhesives, such as pressure-sensitive adhesives, thermally activatedadhesives, or chemical reaction-based adhesives. In some examples thesheets may be bonded by welding techniques such as thermal welding,ultrasonic welding and the like. Sheets may lend themselves to standardindustry practices as roll-to-roll (R2R), or sheet-to-sheet assembly. Asindicted earlier, an interior volume for cathode may need to besubstantially larger than the other active elements in the battery. Muchof a battery construct may have to create the space of this cathodematerial, and support it from migration during flexing of the battery.Another portion of the battery construct that may consume significantportions of the thickness budget may be the separator material. In someexamples, a sheet form of separator may create an advantageous solutionfor laminate processing. In other examples, the separator may be formedby dispensing hydrogel material into a layer to act as the separator.

In these laminate battery assembly examples, the forming product mayhave an anode sheet, which may be a combination of a package layer andan anode current collector, as well as substrate for the anode layer.The forming product may also have an optional separator spacer sheet, acathode spacer sheet, and a cathode sheet. The cathode sheet may be acombination of a package layer and a cathode current collector layer.

Intimate contact between electrodes and current collectors is ofcritical importance for reducing impedance and increasing dischargecapacity. If portions of the electrode are not in contact with thecurrent collector, resistance may increase since conductivity is thenthrough the electrode (typically less conductive than the currentcollector) or a portion of the electrode may become totallydisconnected. In coin cell and cylindrical batteries, intimacy isrealized with mechanical force to crimp the can, pack paste into a can,or through similar means. Wave washers or similar springs are used incommercial cells to maintain force within the battery; however, thesewould add to the overall thickness of a miniature battery. In typicalpatch batteries, a separator may be saturated in electrolyte, placedacross the electrodes, and pressed down by the external packaging. In alaminar, cofacial battery there are several methods to increaseelectrode intimacy. The anode may be plated directly onto the currentcollector rather than using a paste. This process inherently results ina high level of intimacy and conductivity. The cathode; however, istypically a paste. Although binder material present in the cathode pastemay provide adhesion and cohesion, mechanical pressure may be needed toensure the cathode paste remains in contact with the cathode currentcollector. This may be especially important as the package is flexed andthe battery ages and discharges, for example, as moisture leaves thepackage through thin and small seals. Compression of the cathode may beachieved in the laminar, cofacial battery by introducing a compliantseparator and/or electrolyte between the anode and cathode. A gelelectrolyte or hydrogel separator, for example, may compress on assemblyand not simply run out of the battery as a liquid electrolyte would.Once the battery is sealed, the electrolyte and/or separator may thenpush back against the cathode. An embossing step may be performed afterassembly of the laminar stack, introducing compression into the stack.

Exemplary Illustrated Processing of Biocompatible EnergizationElements—Placed Separator

An example of the steps that may be involved in processing biocompatibleenergization elements may be found referring to FIGS. 4A-4N. Theprocessing at some of the exemplary steps may be found in the individualfigures. In FIG. 4A, a combination of a PET Cathode Spacer 401 and a PETGap Spacer 404 may be illustrated. The PET Cathode Spacer 401 may beformed by applying films of PET 403 which, for example, may be roughly 3mils thick. On either side of the PET layer may be found PSA layers orthese may be capped with a PVDF release layer 402 which may be roughly 1mil in thickness. The PET Gap spacer 404 may be formed of a PVDF layer409 which may be roughly 3 mils in thickness. There may be a capping PETlayer 405 which may be roughly 0.5 mils in thickness. Between the PVDFlayer 409 and the capping PET layer 405, in some examples, may be alayer of PSA.

Proceeding to FIG. 4B, a hole 406 in the Gap spacer layer may be cut bylaser cutting treatment. Next at FIG. 4C, the cut PET Gap spacer layermay be laminated 408 to the PET Cathode Spacer layer. Proceeding to FIG.4D, a cathode spacer hole 410 may be cut by laser cutting treatment. Thealignment of this cutting step may be registered to the previously cutfeatures in the PET Gap spacer Layer. At FIG. 4E, a layer of Celgard412, for an ultimate separator layer, may be bonded to a carrier 411.Proceeding to FIG. 4F, the Celgard material may be cut to figures thatare between the size of the previous two laser cut holes, andapproximately the size of the PET gap spacer hole, forming a precutseparator 420. Proceeding to FIG. 4G, a pick and place tool 421 may beused to pick and place discrete pieces of Celgard into their desiredlocations on the growing device. At FIG. 4H, the placed Celgard pieces422 are fastened into place and then the PVDF release layer 423 may beremoved. Proceeding to FIG. 4I, the growing device structure may bebonded to a film of the anode 425. The anode may comprise an anodecollector film upon which a zinc anode film has been electrodeposited.

Proceeding to FIG. 4J, a cathode slurry 430 may be placed into theformed gap. A squeegee 431 may be used in some examples to spread thecathode mix across a work piece and in the process fill the gaps of thebattery devices being formed. After filling, the remaining PVDF releaselayer 432 may be removed which may result in the structure illustratedin FIG. 4K. At FIG. 4L the entire structure may be subjected to a dryingprocess which may shrink the cathode slurry 440 to also be at the heightof the PET layer top. Proceeding to FIG. 4M, a cathode film layer 450,which may already have the cathode collector film upon it, may be bondedto the growing structure. In a final illustration at FIG. 4N a lasercutting process may be performed to remove side regions 460 and yield abattery element 470. There may be numerous alterations, deletions,changes to materials and thickness targets that may be useful within theintent of the present invention.

The result of the exemplary processing may be depicted in some detail atFIG. 5. In an example, the following reference features may be defined.The Cathode chemistry 510 may be located in contact with the cathode andcathode collector 520. A pressure-sensitive adhesive layer 530 may holdand seal the cathode collector 520 to a PET Spacer layer 540. On theother side of the PET Spacer layer 540, may be another PSA layer 550,which seals and adheres the PET Spacer layer 540 to the PET Gap layer560. Another PSA layer 565 may seal and adhere the PET Gap layer 560 tothe Anode and Anode Current Collector layers. A Zinc Plated layer 570may be plated onto the Anode Current Collector 580. The separator layer590 may be located within the structure to perform the associatedfunctions as have been defined in the present invention. In someexamples, an electrolyte may be added during the processing of thedevice, in other examples, the separator may already includeelectrolyte.

Exemplary Processing Illustration of Biocompatible EnergizationElements—Deposited Separator

An example of the steps that may be involved in processing biocompatibleenergization elements may be found in FIGS. 6A-6F. The processing atsome of the exemplary steps may be found in the individual figures.There may be numerous alterations, deletions, changes to materials andthickness targets that may be useful within the intent of the presentinvention.

In FIG. 6A, a laminar construct 600 may be illustrated. The laminarstructure may comprise two laminar construct release layers, 602 and 602a; two laminar construct adhesive layers 604 and 604 a, located betweenthe laminar construct release layers 602 and 602 a; and a laminarconstruct core 606, located between the two laminar construct adhesivelayers 604 and 604 a. The laminar construct release layers, 602 and 602a, and adhesive layers, 604 and 604 a, may be produced or purchased,such as a commercially available pressure-sensitive adhesive transfertape with primary liner layer. The laminar construct adhesive layers maybe a PVDF layer which may be approximately 1-3 millimeters in thicknessand cap the laminar construct core 606. The laminar construct core 606may comprise a thermoplastic polymer resin such as polyethyleneterephthalate, which for example may be roughly 3 millimeters thick.Proceeding to FIG. 6B, a cavity for the cathode pocket 608 may be cut inthe laminar construct by laser cutting treatment.

Next, at FIG. 6C, the bottom laminar construct release layer 602 a maybe removed from the laminar construct, exposing the laminar constructadhesive layer 604 a. The laminar construct adhesive layer 604 a maythen be used to adhere an anode connection foil 610 to cover the bottomopening of the cathode pocket 608. Proceeding to FIG. 6D, the anodeconnection foil 610 may be protected on the exposed bottom layer byadhering a masking layer 612. The masking layer 612 may be acommercially available PSA transfer tape with a primary liner. Next, atFIG. 6E, the anode connection foil 610 may be electroplated with acoherent metal 614, zinc for example, which coats the exposed section ofthe anode connection foil 610 inside of the cathode pocket. Proceedingto 6F, the anode electrical collection masking layer 612 is removed fromthe bottom of the anode connection foil 610 after electroplating.

FIGS. 7A-7F may illustrate an alternate mode of processing the stepsillustrated in FIGS. 6A-6F. FIGS. 7A-7B may illustrate similar processesas depicted in FIGS. 6A-6B. The laminar structure may comprise twolaminar construct release layers, 702 and 702 a, one layer on eitherend; two laminar construct adhesive layers, 704 and 704 a, locatedbetween the laminar construct release layers 702 and 702 a; and alaminar construct core 706, located between the two laminar constructadhesive layers 704 and 704 a. The laminar construct release layers andadhesive layers may be produced or purchased, such as a commerciallyavailable pressure-sensitive adhesive transfer tape with primary linerlayer. The laminar construct adhesive layers may be a polyvinylidenefluoride (PVDF) layer which may be approximately 1-3 millimeters inthickness and cap the laminar construct core 706. The laminar constructcore 706 may comprise a thermoplastic polymer resin such as polyethyleneterephthalate, which for example may be roughly 3 millimeters thick.Proceeding to FIG. 7B, a cavity for the cathode pocket 708 may be cut inthe laminar construct by laser cutting treatment. In FIG. 7C, an anodeconnection foil 710 may be obtained and a protective masking layer 712applied to one side. Next, at FIG. 7D, the anode connection foil 710 maybe electroplated with a layer 714 of a coherent metal, for example,zinc. Proceeding to FIG. 7E, the laminar constructs of FIGS. 7B and 7Dmay be combined to form a new laminar construct as depicted in FIG. 7Eby adhering FIG. 7B to the electroplated layer 714 of FIG. 7D. Therelease layer 702 a of FIG. 7B may be removed in order to exposeadhesive layer 704 a of FIG. 7B for adherence onto electroplated layer714 of FIG. 7D. Proceeding next to FIG. 7F, the anode protective maskinglayer 712 may be removed from the bottom of the anode connection foil710.

FIGS. 8A-8H may illustrate implementation of energization elements to abiocompatible laminar structure, which at times is referred to as alaminar assembly or a laminate assembly herein, similar to, for example,those illustrated in FIGS. 6A-6F and 7A-7F. Proceeding to FIG. 8A, ahydrogel separator precursor mixture 820 may be deposited on the surfaceof the laminate assembly. In some examples, as depicted, the hydrogelprecursor mixture 820 may be applied up a release layer 802. Next, atFIG. 8B, the hydrogel separator precursor mixture 820 may be squeegeed850 into the cathode pocket while being cleaned off of the release layer802. The term “squeegeed” may generally refer to the use of aplanarizing or scraping tool to rub across the surface and move fluidmaterial over the surface and into cavities as they exist. The processof squeegeeing may be performed by equipment similar to the vernacular“Squeegee” type device or alternatively and planarizing device such asknife edges, razor edges and the like which may be made of numerousmaterials as may be chemically consistent with the material to be moved.

The processing depicted at FIG. 8B may be performed several times toensure coating of the cathode pocket, and increment the thickness ofresulting features. Next, at FIG. 8C, the hydrogel separator precursormixture may be allowed to dry in order to evaporate materials, which maytypically be solvents or diluents of various types, from the hydrogelseparator precursor mixture, and then the dispensed and appliedmaterials may be cured. It may be possible to repeat both of theprocesses depicted at FIG. 8B and FIG. 8C in combination in someexamples. In some examples, the hydrogel separator precursor mixture maybe cured by exposure to heat while in other examples the curing may beperformed by exposure to photon energy. In still further examples thecuring may involve both exposure to photon energy and to heat. There maybe numerous manners to cure the hydrogel separator precursor mixture.

The result of curing may be to form the hydrogel separator precursormaterial to the wall of the cathode pocket as well as the surface regionin proximity to an anode or cathode feature which in the present examplemay be an anode feature. Adherence of the material to the sidewalls ofthe cavity may be useful in the separation function of a separator. Theresult of curing may be to form a polymerized precursor mixtureconcentrate 822 which may be simply considered the separator of thecell. Proceeding to FIG. 8D, cathode slurry 830 may be deposited ontothe surface of the laminar construct release layer 802. Next, at FIG. 8Ethe cathode slurry 830 may be squeegeed into the cathode pocket and ontothe anhydrous polymerized precursor mixture concentrate 822. The cathodeslurry may be moved to its desired location in the cavity whilesimultaneously being cleaned off to a large degree from the laminarconstruct release layer 802. The process of FIG. 8E may be performedseveral times to ensure coating of the cathode slurry 830 on top of theanhydrous polymerized precursor mixture concentrate 822. Next, at FIG.8F, the cathode slurry may be allowed to dry down to form an isolatedcathode fill 832 on top of the anhydrous polymerized precursor mixtureconcentrate 822, filling in the remainder of the cathode pocket.

Proceeding to FIG. 8G, an electrolyte formulation 840 may be added on tothe isolated cathode fill 832 and allowed to hydrate the isolatedcathode fill 832 and the anhydrous polymerized precursor mixtureconcentrate 822. Next, at FIG. 8H, a cathode connection foil 816 may beadhered to the remaining laminar construct adhesive layer 804 byremoving the remaining laminar construct release layer 802 and pressingthe connection foil 816 in place. The resulting placement may result incovering the hydrated cathode fill 842 as well as establishingelectrical contact to the cathode fill 842 as a cathode currentcollector and connection means.

FIGS. 9A through 9C may illustrate an alternative example of theresulting laminate assembly from FIG. 7D. In FIG. 9A, the anodeconnection foil 710 may be obtained and a protective masking layer 712applied to one side. The anode connection foil 710 may be plated with alayer 714 of coherent metal with, for example, zinc. In similar fashionas described in the previous figures. Proceeding to FIG. 9B, a hydrogelseparator 910 may be applied without the use of the squeegee methodillustrated in FIG. 8E. The hydrogel separator precursor mixture may beapplied in various manners, for example, a preformed film of the mixturemay be adhered by physical adherence; alternatively, a diluted mixtureof the hydrogel separator precursor mixture may be dispensed and thenadjusted to a desired thickness by the processing of spin coating.Alternatively the material may be applied by spray coating, or any otherprocessing equivalent.

Next, at FIG. 9C, processing is depicted to create a segment of thehydrogel separator that may function as a containment around a separatorregion. The processing may create a region that limits the flow, ordiffusion, of materials such as electrolyte outside the internalstructure of the formed battery elements. Such a blocking feature 920 ofvarious types may therefore be formed. The blocking feature, in someexamples, may correspond to a highly crosslinked region of the separatorlayer as may be formed in some examples by increased exposure to photonenergy in the desired region of the blocking feature 920. In otherexamples, materials may be added to the hydrogel separator materialbefore it is cured to create regionally differentiated portions thatupon curing become the blocking feature 920. In still further examples,regions of the hydrogel separator material may be removed either beforeor after curing by various techniques including for example chemicaletch of the layer with masking to define the regional extent. The regionof removed material may create a blocking feature in its own right oralternatively materially may be added back into the void to create ablocking feature. The processing of the impermeable segment may occurthrough several methods including image out processing, increasedcross-linking, heavy photodosing, back-filling, or omission of hydrogeladherence to create a void. In some examples, a laminate construct orassembly of the type depicted as the result of the processing in FIG. 9Cmay be formed without the blocking feature 920.

Polymerized Battery Element Separators

In some battery designs, the use of a discrete separator (as describedin a previous section) may be precluded due to a variety of reasons suchas the cost, the availability of materials, the quality of materials, orthe complexity of processing for some material options as non-limitingexamples. In such cases, a cast or form-in-place separator which mayhave been depicted in the processes of FIGS. 8A-8H, for example, mayprovide desirable benefits. While starch or pasted separators have beenused commercially with success in AA and other format Leclanché orzinc-carbon batteries, such separators may be unsuitable in some waysfor use in certain examples of laminar microbatteries. Particularattention may need to be paid to the uniformity and consistency ofgeometry for any separator used in the batteries of the presentinvention. Precise control over separator volume may be needed tofacilitate precise subsequent incorporation of known cathode volumes andsubsequent realization of consistent discharge capacities and cellperformance.

A method to achieve a uniform, mechanically robust form-in-placeseparator may be to use UV-curable hydrogel formulations. Numerouswater-permeable hydrogel formulations may be known in variousindustries, for example, the contact lens industry. An example of acommon hydrogel in the contact lens industry may bepoly(hydroxyethylmethacrylate) crosslinked gel, or simply pHEMA. Fornumerous applications of the present invention, pHEMA may possess manyattractive properties for use in Leclanché and zinc-carbon batteries.pHEMA typically may maintain a water content of approximately 30-40% inthe hydrated state while maintaining an elastic modulus of about 100 psior greater. Furthermore, the modulus and water content properties ofcrosslinked hydrogels may be adjusted by one of skill in the art byincorporating additional hydrophilic monomeric (e.g. methacrylic acid)or polymeric (e.g. polyvinylpyrrolidone) components. In this manner, thewater content, or more specifically, the ionic permeability of thehydrogel may be adjusted by formulation.

Of particular advantage in some examples, a castable and polymerizablehydrogel formulation may contain one or more diluents to facilitateprocessing. The diluent may be chosen to be volatile such that thecastable mixture may be squeegeed into a cavity, and then allowed asufficient drying time to remove the volatile solvent component. Afterdrying, a bulk photopolymerization may be initiated by exposure toactinic radiation of appropriate wavelength, such as blue UV light at420 nm, for the chosen photoinitiator, such as CG 819. The volatilediluent may help to provide a desirable application viscosity so as tofacilitate casting a uniform layer of polymerizable material in thecavity. The volatile diluent may also provide beneficial surface tensionlowering effects, particularly in the case where strongly polar monomersare incorporated in the formulation. Another aspect that may beimportant to achieve the casting of a uniform layer of polymerizablematerial in the cavity may be the application viscosity. Common smallmolar mass reactive monomers typically do not have very highviscosities, which may be typically only a few centipoise. In an effortto provide beneficial viscosity control of the castable andpolymerizable separator material, a high molar mass polymeric componentknown to be compatible with the polymerizable material may be selectedfor incorporation into the formulation. Examples of high molar masspolymers which may be suitable for incorporation into exemplaryformulations may include polyvinylpyrrolidone and polyethylene oxide.

In some examples the castable, polymerizable separator may beadvantageously applied into a designed cavity, as previously described.In alternative examples, there may be no cavity at the time ofpolymerization. Instead, the castable, polymerizable separatorformulation may be coated onto an electrode-containing substrate, forexample, patterned zinc plated brass, and then subsequently exposed toactinic radiation using a photomask to selectively polymerize theseparator material in targeted areas. Unreacted separator material maythen be removed by exposure to appropriate rinsing solvents. In theseexamples, the separator material may be designated as aphoto-patternable separator.

Multiple Component Separator Formulations

The separator, useful according to examples of the present invention,may have a number of properties that may be important to its function.In some examples, the separator may desirably be formed in such a manneras to create a physical barrier such that layers on either side of theseparator do not physically contact one another. The layer may thereforehave an important characteristic of uniform thickness, since while athin layer may be desirable for numerous reasons, a void or gap freelayer may be essential. Additionally, the thin layer may desirably havea high permeability to allow for the free flow of ions. Also, theseparator requires optimal water uptake to optimize mechanicalproperties of the separator. Thus, the formulation may contain acrosslinking component, a hydrophilic polymer component, and a solventcomponent.

A crosslinker may be a monomer with two or more polymerizable doublebonds. Suitable crosslinkers may be compounds with two or morepolymerizable functional groups. Examples of suitable hydrophiliccrosslinkers may also include compounds having two or more polymerizablefunctional groups, as well as hydrophilic functional groups such aspolyether, amide or hydroxyl groups. Specific examples may includeTEGDMA (tetraethyleneglycol dimethacrylate), TrEGDMA (triethyleneglycoldimethacrylate), ethyleneglycol dimethacylate (EGDMA), ethylenediaminedimethyacrylamide, glycerol dimethacrylate and combinations thereof.

The amounts of crosslinker that may be used in some examples may range,e.g., from about 0.000415 to about 0.0156 mole per 100 grams of reactivecomponents in the reaction mixture. The amount of hydrophiliccrosslinker used may generally be about 0 to about 2 weight percent and,for example, from about 0.5 to about 2 weight percent. Hydrophilicpolymer components capable of increasing the viscosity of the reactivemixture and/or increasing the degree of hydrogen bonding with theslow-reacting hydrophilic monomer, such as high molecular weighthydrophilic polymers, may be desirable.

The high molecular weight hydrophilic polymers provide improvedwettability, and in some examples may improve wettability to theseparator of the present invention. In some non-limiting examples, itmay be believed that the high molecular weight hydrophilic polymers arehydrogen bond receivers which in aqueous environments, hydrogen bond towater, thus becoming effectively more hydrophilic. The absence of watermay facilitate the incorporation of the hydrophilic polymer in thereaction mixture. Aside from the specifically named high molecularweight hydrophilic polymers, it may be expected that any high molecularweight polymer will be useful in this invention provided that when thepolymer is added to an exemplary silicone hydrogel formulation, thehydrophilic polymer (a) does not substantially phase separate from thereaction mixture and (b) imparts wettability to the resulting curedpolymer.

In some examples, the high molecular weight hydrophilic polymer may besoluble in the diluent at processing temperatures. Manufacturingprocesses which use water or water soluble diluents, such as isopropylalcohol (IPA), may be desirable examples due to their simplicity andreduced cost. In these examples, high molecular weight hydrophilicpolymers which are water soluble at processing temperatures may also bedesirable examples.

Examples of high molecular weight hydrophilic polymers may include butare not limited to polyamides, polylactones, polyimides, polylactams andfunctionalized polyamides, polylactones, polyimides, polylactams, suchas PVP and copolymers thereof, or alternatively, DMA functionalized bycopolymerizing DMA with a lesser molar amount of a hydroxyl-functionalmonomer such as HEMA, and then reacting the hydroxyl groups of theresulting copolymer with materials containing radical polymerizablegroups. High molecular weight hydrophilic polymers may include but arenot limited to poly-N-vinyl pyrrolidone, poly-N-vinyl-2-piperidone,poly-N-vinyl-2-caprolactam, poly-N-vinyl-3-methyl-2-caprolactam,poly-N-vinyl-3-methyl-2-piperidone, poly-N-vinyl-4-methyl-2-piperidone,poly-N-vinyl-4-methyl-2-caprolactam, poly-N-vinyl-3-ethyl-2-pyrrolidone,and poly-N-vinyl-4,5-dimethyl-2-pyrrolidone, polyvinylimidazole,poly-N—N-dimethylacrylamide, polyvinyl alcohol, polyacrylic acid,polyethylene oxide, poly 2 ethyl oxazoline, heparin polysaccharides,polysaccharides, mixtures and copolymers (including block or random,branched, multichain, comb-shaped or star-shaped) thereof wherepoly-N-vinylpyrrolidone (PVP) may be a desirable example where PVP hasbeen added to a hydrogel composition to form an interpenetrating networkwhich shows a low degree of surface friction and a low dehydration rate.

Additional components or additives, which may generally be known in theart may also be included. Additives may include but are not limited toultra-violet absorbing compounds, photo-initiators such as CGI 819,reactive tints, antimicrobial compounds, pigments, photochromic, releaseagents, combinations thereof and the like.

The method associated with these types of separators may also includereceiving CGI 819; then mixing with PVP, HEMA, EGDMA and IPA; and thencuring the resulting mixture with a heat source or an exposure tophotons. In some examples the exposure to photons may occur where thephotons' energy is consistent with a wavelength occurring in theultraviolet portion of the electromagnetic spectrum. Other methods ofinitiating polymerization generally performed in polymerizationreactions are within the scope of the present invention.

The biocompatible devices may be, for example, implantable electronicdevices, such as pacemakers and micro-energy harvesters, electronicpills for monitoring and/or testing a biological function, surgicaldevices with active components, ophthalmic devices, microsized pumps,defibrillators, stents, and the like.

Specific examples have been described to illustrate sample embodimentsfor the formation, methods of formation, and apparatus of formation ofbiocompatible energization elements composing separators. These examplesare for the illustration and are not intended to limit the scope of theclaims in any manner. Accordingly, the description is intended toembrace all examples that may be apparent to those skilled in the art.

1) A battery comprising: a first and second electrode; an anode; acathode; and a separator comprising a permeable silicone hydrogelmembrane wherein the separator is a polymerized layer mixturecomprising: a water soluble polymer/polymeric component; a firstpolymerizable monomer; a second polymerizable monomer; and a liquidsolvent. 2) The battery of claim 1 wherein the water solublepolymer/polymeric component is polyvinylpyrrolidone (PVP). 3) Thebattery of claim 1 wherein the first polymerizable monomer is ahydrophobic polymer with hydrophilic pendant group. 4) The battery ofclaim 3 wherein the hydrophobic polymer with hydrophilic pendant groupis hydroxyethylmethacrylate (HEMA). 5) The battery of claim 1 whereinthe second polymerizable monomer is a diester crosslinking agent. 6) Thebattery of claim 5 wherein the diester crosslinking agent is ethyleneglycol dimethylacrylate (EGDMA). 7) The battery of claim 1 wherein theliquid solvent is isopropyl alcohol (IPA). 8) A battery comprising: afirst and second electrode; an anode; a cathode; and a separatorcomprising a permeable silicone hydrogel membrane wherein the separatoris a polymerized mixture comprising: hydroxyethyl methacrylate (HEMA);ethylene glycol dimethylacrylate (EGDMA); polyvinylpyrrolidone (PVP);and isopropyl alcohol (IPA). 9-29) (canceled)